Viewing posts categorised under: Hydrogen fuel systems for cars

Importance of secure strong Electrical Terminals and connections

hydrogen fuel systems for cars

Electrical Terminals

Many people have asked me “how important is it make all electrical  terminals secure ?”

My answer is  always “good electrical terminals and junctions must always be perfect, if not welded terminals, so as to reduce / stop energy losses,,, energy that must be used to generate hydrogen rather than produce heat”

The oxidation/ reduction potential of water to produce hydrogen gas is Locked by Science, Locked by Chemical Thermodynamics, Locked by Electrochemistry, Locked by God (Im not meaning to sacrilegious)  If you do not arrange your system to use this REDOX voltage per cell, then all you will produce is steam.  If you want steam then use a Kettle.

Electrolysis of water is the decomposition of water into oxygen and hydrogen gas due to an electric current passed through the water. The reaction has a standard potential of −1.23 V, meaning it ideally requires a potential difference of 1.23 volts to split water

The potential difference of 1.23 volts, is the absolute minimum voltage per cell for the electrolytic reaction, but then there is the voltage required to overcome the internal resistance of the solution.  When everything is taken into account , then 2.2 volts per cell is required to produce hydrogen and oxygen gas in electrolysis.    If fail to provide 2.2 volts for each cell in the system then you cannot produce Hydrogen gas.

Take for example a case when the faulty terminals use 0.4 volts as heat, the voltage drop due to internal resistance of the solution is always 1 volt and therefore less than 1.23 volts is available for the REDOX reaction to produce hydrogen gas.  All you produce is steam

Does this explain the importance of making sure that all electrical terminals are secure and do not waste input voltage as heat

Hydrogen fuel systems pty ltd has solved many terminal risks by MIG welding terminals.  Eg all electrolysis connections in the cells are Mig welded , not just bolted together

In the case of wire junctions that cannot be welded, the bare copper wires must be protected from oxidation and corrosion by  coating wires with protective fluids such as lanoline.  Hydrogen fuel systems also protect wire  connections and at reduce internal resistance of connections by using power ratchet crimpers  and  soldering all crimped wires to connecting terminals


As I have discussed before the key fault of these “Neutral plate arrangements” sold by majority of USA “Hydrogen producer companies” is that many of these companies use up to 101  plates to try and get more gas produced.  These make believe Chemists fail to understand that at 101 plates they actually are trying to have 100 cells.  To get 100 cells operating you need an input voltage of 220 volts…. From a car that only uses a 12 volt battery…. What these cells make is steam and lots of it.

If they use a voltage inverter to ramp up 220 volts and then use 30 amp to make gas then they are trying to get their  battery to generate 220 x 30 = 6600 watts of electrical power…. This is impossible

Call me on 0403177183 or  if you would like to learn more.  I am a registered teacher, Physicist, Chemist and Engineer,,, not a “would be, could be” pretend Scientist

Kind regards

Gavan Knox

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New Agents wanted… Excellent Commisions paid

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As Managing director  of Hydrogen fuel systems pty ltd, I have decided to make an offer to individuals who wish to increase their income by acting as agents for the company and promoting the sale and distribution of these patented Systems throughout their district and the world at large.

I am supported by other board members of my company in making this offer which is an excellent way of getting in at the ” ground floor” of this  excellent and exciting technology. I offer agents $400 for every system that they manage to sell to individuals / or companies .  A trucking company typically uses two of the Gen 20 systems to power their trucks  ( ove 10 litre engine capacity)  and therefore earns $800 per truck for the agent who arranged the sale of the systems

In order to complete the transaction the agent must first of all read sign and return to me an agency agreement form and confidentiality agreement form. Having completed the forms, My secretary / company solicitor stores the documents.  Our company secretary then deposites the agent commmission directly into the agents bank , by electronic funds transfer, once the purchase  has been completed by the new client.

The agent will need to provide their  full name ,address and bank account details so that funds can be quickly transferred into their account .   If the agent is an Australian Citizen these funds must be treated as income and declared to the taxation department.

Agents need to specify then regions where they feel they can comfortably  and effectively service.   It si also advisable to work with a local automotive electrician , who can follow the instructions for installation shown on the site listed                 to promptly install the systems on clients vehicles.   Agents can also earn a living by working with the auto elecrician in the installation procedure.

These systems , we produce , are patented making them a rarity in this industry  and proving the systems we produce actually work.   We are not aiming to produce “Free energy”…. it does not exist . Rather we aim in increasing fuel efficiency and reduce engine maintenance costs as well as increase engine outupt Power and torque

Please share this post with friends and family.  Lets try and make the most of this technology which is able to reduce the costs of running an internal combustion engine

I can be contacted on mobile phone 61 0403177183

Gavan Knox – BSc (Physics), BSc (Chemistry), BEng (Civil), MEng (Chemical/ Metallugy), BEd (Physics, Chemistry, Mathematics)

Managing Director “Hydrogenfuelsystems pty ltd”  (mobile)

61 0403177183

How Does hydrogen hho, fuel , power, thermodynamics, efficiency, Oxygen increase fuel economy in an engine

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How Does Hydrogen/ Oxygen  Work in an internal combustion engine?

Hydrogen. I get asked this question a lot. And yet, this is the most important point to understand if you want to make your car more fuel efficient using this technology. The underlying physics and chemistry/ chemical thermodynamics  of this subject can be very complicated. But fortunately the basic concepts are very few and extremely simple.

Misconception of the use of burning hydrogen in you engine

Many people think that we are generating Hydrogen so we can burn it, and that burning this HYDROGEN adds so much power, that we get better fuel mileage. In actual fact, this is not the case. To prove this point, lets this a step further. There are 3 energy conversions at work here:

  • Mechanical to electrical (the alternator generates electrical energy)
  • Electrical to chemical (the cell makes hydrogen from electro-chemical  energy)
  • Chemical to mechanical (the Hydrogen  burns in the engine to make mechanical energy)

The problem is that there are 3 energy conversions occurring here, and each one loses some energy – in agreement with the third law of chemical thermodynamics.    It is a basic fundamental of physics that in any conversion of energy from one form to another, there is going to be some loss.

Engine Efficiency using hydrogen

There is no such thing as 100% efficiency. In some of these conversions there is quite a bit of loss. So if this is all there was to the picture, then the system would actually lose mileage.

I’ve seen this mistaken idea expressed in magazines and on television news coverage to prove that Hydrogen on demand  doesn’t work.

What Really Is Going On inside your engine when you burn hydrogen in your engine?

Well, if we aren’t trying to burn the HYDROGEN to get our fuel economy, then how does it work?

In actual fact, HYDROGEN, when added to the air/fuel mixture going into the engine, causes that petroleum fuel to burn more completely and thereby releasing more of the energy of the fuel that would otherwise be wasted. The way this is done is by speeding up the burning process in the cylinder. Scientists say that it considerably increases the flame speed of the petroleum mixture. And it is this fact that sums up the primary way that HYDROGEN improves fuel mileage.

Flame speed

When the flame speed of the fuel mixture is increased, the fuel is burned completely during the power stroke and closer to top dead centre.  Less fuel is being burned after the power stroke, which is the exhaust stroke, and which actually works against the turning of the engine.

Further, less unburned fuel is being expelled from the engine as waste and pollutants. A relatively small amount of HYDROGEN will have a dramatic impact on the amount of power a given amount of gasoline will produce. This will then increase fuel mileage dramatically, and cut out a large fraction of the amount of harmful emissions the engine produces.

Hydrogen technology Summary

There is a remarkable simplicity to this technology. If you add HYDROGEN to your engine, you will get an increase in combustion efficiency. That is just science, and it works as certainly as turning on a light switch. In some cases with modern cars and pickup trucks, we need to make some adjustments to the computer so it will allow these savings to take place. But with most commercial large engine systems, such as truck engines, gensets, marine engines, etc, no other handling is needed to get these remarkable fuel savings. To purchase one of these systems, please email or

youtube videos by hydrogenfuelsystems pty ltd

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YOUtube channel hydrogenfuelystems

Check out other youtube videos from  hydrogenfuelsystems australia and see how they are arranged for use on Trucks, Cars, Mining equipment, Farming Engines Gensets, Boating, Trawlers and Shipping.

Link to the 41 youtube videos by hydrogenfuelsystems pty ltd

Wideband Oxygen Sensors and Air/Fuel (A/F) Sensors

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Wideband Oxygen sensor

Wideband Oxygen Sensor (which may also be called Wide Range Air Fuel (WRAF) sensors) and Air/Fuel (A/F) Sensors, are replacing conventional oxygen sensors in many late model vehicles.

A wideband O2 sensor or A/F sensor is essentially a smarter oxygen sensor with some additional internal circuitry that allows it to precisely determine the exact air/fuel ratio of the engine. Like an ordinary oxygen sensor, it reacts to changing oxygen levels in the exhaust. But unlike an ordinary oxygen sensor, the output signal from a wideband O2 sensor or A/F sensor does not change abruptly when the air/fuel mixture goes rich or lean. This makes it better suited to today’s low emission engines, and also for tuning performance engines.


Oxygen Sensor Outputs

An ordinary oxygen sensor is really more of a rich/lean indicator because its output voltage jumps up to 0.8 to 0.9 volts when the air/fuel mixture is rich, and drops to 0.3 volts or less when the air/fuel mixture is lean. By comparison, a wideband O2 sensor or A/F sensor provides a gradually changing current signal that corresponds to the exact air/fuel ratio.

Another difference is that the sensor’s output voltage is converted by its internal circuitry into a variable current signal that can travel in one of two directions (positive or negative). The current signal gradually increases in the positive direction when the air/fuel mixture becomes leaner. At the “stoichiometric” point when the air/fuel mixture is perfectly balanced (14.7 to 1), which is also referred to as “Lambda”, the current flow from the sensor stops and there is no current flow in either direction. And when the air/fuel ratio becomes progressively richer, the current reverses course and flows in the negative direction.


The PCM sends a control reference voltage (typically 3.3 volts on Toyota A/F sensor applications, 2.6 volts on Bosch and GM wideband sensors) to the sensor through one pair of wires, and monitors the sensor’s output current through a second set of wires. The sensor’s output signal is then processed by the PCM, and can be read on a scan tool as the air/fuel ratio, a fuel trim value and/or a voltage value depending on the application and the display capabilities of the scan tool.

For applications that display a voltage value, anything less than the reference voltage indicate a rich air/fuel ratio while voltages above the reference voltage indicates a lean air/fuel ratio. On some of the early Toyota OBD II applications, the PCM converts the A/F sensor voltage to look like that of an ordinary oxygen sensor (this was done to comply with the display requirements of early OBD II regulations).

How a Wideband O2 Sensor Works

Internally, wideband O2 sensors and A/F sensors appear to be similar to conventional zirconia planar oxygen sensors. There is a flat ceramic strip inside the protective metal nose cone on the end of the sensor. The ceramic strip is actually a dual sensing element that combines a “Nerst effect” oxygen pump and “diffusion gap” with the oxygen sensing element. All three are laminated on the same strip of ceramic.


Exhaust gas

Exhaust gas enters the sensor through vents or holes in the metal shroud over the tip of the sensor and reacts with the dual sensor element. Oxygen diffuses through the ceramic substrate on the sensor element. The reaction causes the Nerst cell to generate a voltage just like an ordinary oxygen sensor. The oxygen pump compares the change in voltage to the control voltage from the PCM, and balances one against the other to maintain an internal oxygen balance. This alters the current flow through the sensor creating a positive or negative current signal that indicates the exact air/fuel ratio of the engine.

The current flow is not much, usually only about 0.020 amps or less. The PCM then converts the sensor’s analog current output into a voltage signal that can then be read on your scan tool.

What’s the difference between a wideband O2 sensor and an A/F sensor? Wideband 2 sensors typically have 5 wires while most A/F sensors have 4 wires.


Like ordinary oxygen sensors, wideband O2 sensors and A/F sensors also have an internal heater circuit to help them reach operating temperature quickly. To work properly, wideband and A/F sensors require a higher operating temperature: 1292 to 1472 degrees F versus about 600 degrees F for ordinary oxygen sensors. Consequently, if the heater circuit fails, the sensor may not put out a reliable signal.

The heater circuit is energized through a relay, which turns on when the engine is cranked and the fuel injection relay is energized. The heater circuit can pull up to 8 amps on some engines, and is usually pulse width modulated (PWM) to vary the amount of heat depending on engine temperature (this also prevents the heater from getting too hot and burning out). When the engine is cold, the duty ratio (on time) of the heater circuit will be higher than when the engine is hot. A failure in the heater circuit will usually turn on the Malfunction Indicator Lamp (MIL) and set a P0125 diagnostic trouble code (DTC).


Oxygen Sensor Problems

Like ordinary oxygen sensors, wideband O2 sensors and A/F sensors are vulnerable to contamination and aging. They can become sluggish and slow to respond to changes in the air/fuel mixture as contaminants build up on the sensor element. Contaminants include phosphorus from motor oil (from worn valve guides and rings), silicates from antifreeze (leaky head gasket or intake gaskets, or cracks in the combustion chamber that leak coolant), and even sulfur and other additives in gasoline. The sensors are designed to last upwards of 200,000 km but may not go the distance if the engine burns oil, develops an internal coolant leak or gets some bad gas.

Wideband 2 sensors and A/F sensors can also be fooled by air leaks in the exhaust system (leaky exhaust manifold gaskets) or compression problems (such as leaky or burned exhaust valves) that allow unburned air to pass through the engine and enter the exhaust.

Wideband A/F Sensor Diagnostics

As a rule, the OBD II system will detect any problems that affect the operation of the oxygen or A/F sensors and set a DTC that corresponds to the type of fault. Generic OBD II codes that indicate a fault in the O2 or A/F sensor heater circuit include: P0036, P0037, P0038, P0042, P0043, P0044, P0050, P0051, P0052, P0056, P0057, P0058, P0062, P0063, P0064.

Codes that indicate a possible fault in the oxygen sensor itself include any code from P0130 to P0167. There may be additional OEM “enhanced “P1” codes that will vary depending on the year, make and model of the vehicle.

The symptoms of a bad wideband O2 sensor or A/F sensor are essentially the same as those of a conventional oxygen sensor: Engine running rich, poor fuel economy and/or an emission failure due to higher than normal levels of carbon monoxide (CO) in the exhaust.

Possible causes in addition to the sensor itself having failed

Possible causes in addition to the sensor itself having failed include bad wiring connections or a faulty heater circuit relay (if there are heater codes), or a wiring fault, leaky exhaust manifold gasket or leaky exhaust valves if there are sensor codes indicating a lean fuel condition.

What to Check: How the sensor responds to changes in the air/fuel ratio. Plug a scan tool into the vehicle diagnostic connector, start the engine and create a momentary change in the air/fuel radio by snapping the throttle or feeding propane into the throttle body. Look for a response from the wideband O2 sensor or A/F sensor. No change in the indicated air/fuel ratio, Lambda value, sensor voltage value or short term fuel trim number would indicate a bad sensor that needs to be replaced.

Scan tool

Other scan tool PIDS to look at include the OBD II oxygen heater monitor status, OBD II oxygen sensor monitor status, loop status and coolant temperature. The status of the monitors will tell you if the OBD II system has run its self-checks on the sensor. The loop status will tell you if the PCM is using the wideband O2 or A/F sensor’s input to control the air/fuel ratio. If the system remains in open loop once the engine is warm, check for a possible faulty coolant sensor.

Another way to check the output of a wideband O2 sensor or A/F sensor is to connect a digital voltmeter or graphing multimeter in series with the sensor’s voltage reference line (refer to a wiring diagram for the proper connection). Connect the black negative lead to the sensor end of the reference wire, and the red positive lead to the PCM end of the wire. The meter should then show an increase in voltage (above the reference voltage) if the air/fuel mixture is lean, or a drop in voltage (below the reference voltage) if the mixture is rich.

Wideband O2 sensor output

The output of a wideband O2 sensor or A/F sensor can also be observed on a digital storage oscilloscope by connecting one lead to the reference circuit and the other to the sensor control circuit. This will generate a waveform that changes with the air/fuel ratio. The scope can also be connected to the sensor’s heater wires to check the duty cycle of the heater circuit. You should see a square wave pattern and a decrease in the duty cycle as the engine warms up.

Wideband Oxygen Sensor Tech Tips

* On Honda 5-wire “Lean Air Fuel” (LAF) sensors, the 8-pin connector pin for the sensor contains a special “calibration” resistor. The value of the resistor can be determined by measuring between terminals 3 and 4 with an ohmmeter, and will be 2.4K ohms, 10K ohms or 15k ohms depending on the application. If the connector is damaged and must be replaced, the replacement must have the same value as the original. The reference voltage from the PCM to the sensor on these engines is 2.7 volts.

* Saturn also uses a special trim resistor in their wideband O2 sensor connector (pins 1 & 6). The resistor is typically 30 to 300 ohms. The PCM supplied reference voltage is 2.4 to 2.6 volts.

* If a O2 sensor, wideband O2 sensor or A/F sensor has failed because of coolant contamination, do not replace the sensor until the leaky head gasket or cylinder head has been replaced. The new sensor will soon fail unless the coolant leak is fixed.

* Some early Toyota applications with A/F sensors provide a “simulated” O2 sensor voltage to be displayed on a scan tool. The actual value was divided by 5 to comply with early OBD II regulations. Those regulations have since been revised, but be aware if you get a “funky” display on your scan tool

Mass Airflow MAF Sensors

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Mass Airflow  Sensors



Copyright AA1Car

Mass airflow sensors  MAF, which are used on a variety of multiport fuel injection systems, come in two basic varieties: hot wire and hot film. Though slightly different in design, both types of sensors measure the volume and density of the air entering the engine so the computer can calculate how much fuel is needed to maintain the correct fuel mixture.

Mass airflow sensors have no moving parts. Unlike a vane airflow meter that uses a spring-loaded flap, mass airflow sensors use electrical current to measure airflow. The sensing element, which is either a platinum wire (hot wire) or nickel foil grid (hot film), is heated electrically to keep it a certain number of degrees hotter than the incoming air. In the case of hot film MAFs, the grid is heated to 75 degrees C. above incoming ambient air temperature. With the hot wire sensors, the wire is heated to 100 degrees C. above ambient temperature. As air flows past the sensing element, it cools the element and increases the current needed to keep the element hot. Because the cooling effect varies directly with the temperature, density and humidity of the incoming air, the amount of current needed to keep the element hot is directly proportional to the air “mass” entering the engine.



Mass airflow sensors MAF sensor output to the computer depends on the type of sensor used. The hot wire version, which Bosch introduced back in ’79 on its LH-Jetronic fuel injection systems and is used on a number of multiport systems including GM’s 5.0L and 5.7L Tuned Port Injection (TPI) engines, generates an analog voltage signal that varies from 0 to 5 volts. Output at idle is usually 0.4 to 0.8 volts increasing up to 4.5 to 5.0 volts at wide open throttle.

The hot film MAFs, which AC Delco introduced in ’84 on the Buick turbo V6 and have since used on the 2.8, 3.0 and 3.8L V6 engines, produce a square wave variable frequency output. The frequency range varies from 30 to 150 Hz, with 30 Hz being average for idle and 150 Hz for wide open throttle.

fig 1- Digital MAF waveform

Another difference between the hot wire and hot film sensors is that the Bosch hot wire units have a self-cleaning cycle where the platinum wire is heated to 1000 degrees C. for one second after the engine is shut down. The momentary surge in current is controlled by the onboard computer through a relay to burn off contaminants that might otherwise foul the wire and interfere with the sensor’s ability to read incoming air mass accurately.

Fig 2.- engine performance monitor


An engine with a bad MAF sensor may start and stall or be hard to start, it may hesitate under load, idle rough or run excessively rich or lean. The engine may also hiccup when the throttle suddenly changes position.

Often, a dirty or faulty MAF sensor will cause the engine to set a LEAN code and turn on the Check Engine Light. If the MAF sensor wire becomes dirty or is contaminated with oil (from an aftermarket reusable air filter), it will be slow to react to changes in airflow. This may cause the MAF sensor to under-report airflow, causing the engine to run lean.

On OBD II vehicles, the input from the MAF sensor is combined with those form the throttle position sensor, MAP sensor and engine speed to calculate engine load. If your scan tool can display calculated engine load, look at the value to see if the load is low at idle, and higher when the engine is running under load. No change in the reading or a reading that makes no sense could indicate a problem with any of these sensors.

If you suspect a MAF sensor problem, scan for any fault codes. Trouble codes that may indicate a problem with the mass airflow sensor include:

P0100….Mass or Volume Air Flow Circuit

P0101….Mass or Volume Air Flow Circuit Range/Performance Problem

P0102….Mass or Volume Air Flow Circuit Low Input

P0103….Mass or Volume Air Flow Circuit High Input

P0104….Mass or Volume Air Flow Circuit Intermittent

P0171….System too Lean (Bank 1)

P0172….System too Rich (Bank 1)

P0173….Fuel Trim Malfunction (Bank 2)

P0174….System too Lean (Bank 2)

P0175….System too Rich (Bank 2)

On older Pre-OBD II vehicles, you can use a scan tool or manual flash code procedure to read the codes:

GM Pre-OBD II: Code 33 (too high frequency) and Code 34 (too low frequency) on engines with multiport fuel injection only, and Code 36 on 5.0L and 5.7L engines that use the Bosch hot wire MAF if the burn-off cycle after shut-down fails to occur.

Ford Pre-OBD II: Code 26 (MAF out of range), Code 56 (MAF output too high), Code 66 (MAF output too low), and Code 76 (no MAF change during “goose” test).

Of course, don’t overlook the basics, too such as engine compression, vacuum, fuel pressure, ignition, etc., since problems in any of these areas can produce similar driveability symptoms.



Unlike vane airflow meters with their movable flaps, MAFs have no moving parts so the only way to know if the unit is functioning properly is to look at the sensor’s output, or its effect on injector timing.

With the Bosch hot wire sensors, sensor voltage output can be read directly with a digital voltmeter by probing the appropriate terminals. If the voltage readings are out of range, or if the sensor’s voltage output fails to increase when the throttle is opened with the engine running, the sensor is defective and needs to be replaced. A dirty wire (which may be the result of a defective self-cleaning circuit or external contamination of the wire) can make the sensor slow to respond to changes in airflow. A broken or burned out wire would obviously prevent the sensor from working at all. Power to the MAF sensor is provided through a pair of relays (one for power, one for the burn-off cleaning cycle), so check the relays first if the MAF sensor appears to be dead or sluggish.

Vibration-related sensor problems

On GM MAF sensors, there are a couple of quick checks you can do for vibration-related sensor problems. Attach an analog voltmeter to the appropriate MAF sensor output terminal. With the engine idling, the sensor should be putting out a steady 2.5 volts. Tap lightly on the sensor and note the meter reading. A good sensor should show no change. If the analog needle jumps and/or the engine momentarily misfires, the sensor is bad and needs to be replaced. You can also check for heat-related problems by heating the sensor with a hair dryer and repeating the test.

This same test can also be done using a meter that reads frequency. The older AC Delco MAF sensors (like a 2.8L V6) should show a steady reading of 30 to 50 Hz at idle and 70 to 75 Hz at 3,500 rpm. The later model units (like those on a 3800 V6) should read about 2.9 kHz at idle and 5.0 kHz at 3,500 rpm. If tapping on the MAF sensor produces a sudden change in the frequency signal, it’s time for a new sensor.

On the GM hot film MAFs, you can also tap into the onboard computer data stream with a scan tool to read the MAF sensor output in “grams per second” (GPS). The reading might go from 3 to 5 GPS at idle up to 100 to 240 GPS at wide open throttle and 5000 RPM.

The scantool GPS reading at idle will vary by engine displacement. The larger the engine, the higher the GPS reading at idle. The GPS idle reading will roughly correspond to engine displacement in liters. A 3.0L V6 engine, for example, will generate a GPS reading of about 3.0 grams per second at idle. A larger 5.0L V8 would read around 5 grams per second, and a smaller 2.0L four cylinder would read around 2 grams per second at idle.

published MAF sensor GPS reading specification

Some vehicle manufacturers publish MAF sensor GPS reading specifications for specific engine speeds. The engine is held steady at the specified RPM to compare the scantool GPS reading to the spec. If the reading is off by more than 10 percent, the MAF sensor is not reading airflow correctly. The cause could be a dirty sensor that needs to be cleaned.

Fig 3 – Bosch Hot wire MAF waveform

Like throttle position sensors, there should be smooth linear transition in sensor output throughout the rpm range. If the readings jump all over the place, the computer won’t be able to deliver the right air/fuel mixture and driveability and emissions will suffer. So you should also check the sensor’s output at various speeds to see that it’s output changes appropriately. This can be done by graphing its frequency output every 500 rpm, or by observing the sensor’s waveform on a scope. The waveform should be square and show a gradual increase in frequency as engine speed and load increase. Any skips or sudden jumps or excessive noise in the pattern would tell you the sensor needs to be replaced.

MAF sensor output

Another way to check MAF sensor output is to see what effect it is has on injector timing. Using an oscilloscope or multimeter that reads milliseconds, connect the test probe to any injector ground terminal (one injector terminal is the supply voltage and the other is the ground circuit to the computer that controls timing). Then look at the duration of the injector pulses at idle (or while cranking the engine if the engine won’t start). Injector timing varies depending on the application, but if the mass airflow sensor is not producing a signal, injector timing will be about four times longer than normal (possibly making the fuel mixture too rich to start). You can also use millisecond readings to confirm fuel enrichment when the throttle is opened during acceleration, fuel leaning during light load cruising and injector shut-down during deceleration. Under light load cruise, for example, you should see about 2.5 to 2.8 Ms duration.

Fig 4 —  Ford Mass airflow sensor


For some reason, Ford vehicles have had a history of MAF sensor problems caused by contamination. In some cases, dirt gets past a leaky air filter and fouls the sensor wire. In other cases, carbon varnish builds up on the sensor from fuel vapors backing up through the intake manifold. Either way, contamination makes the MAF sens3B”>

The engine coolant temperature Sensors

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The engine coolant temperature (ECT) Sensor

The engine coolant temperature (ECT) sensor is a relatively simple sensor that monitors the internal temperature of the engine. Coolant inside the engine block and cylinder head(s) absorbs heat from the cylinders when the engine is running. The coolant sensor detects the change in temperature and signals the Powertrain Control Module (PCM) so it can tell if the engine is cold, warming up, at normal operating temperature or overheating.

The coolant sensor is extremely important because the sensor’s input to the PCM affects the operating strategy of the entire engine management system. That’s why the coolant sensor is often called the “master” sensor.

Many of the fuel, ignition, emissions and drivetrain functions handled by the PCM are affected by the engine’s operating temperature. A different operating strategy is used when the engine is cold than when it is warm. This is done to improve cold driveability, idle quality and emissions. Consequently, if the coolant sensor fails or is giving the PCM a false reading, it can upset a lot of things.



Input from the coolant sensor may be used by the PCM for any or all of the following control functions:

  1. Start up fuel enrichment on fuel injected engines. When the PCM receives a cold signal from the coolant sensor, it increases injector pulse width (on time) to create a richer fuel mixture. This improves idle quality and prevents hesitation while the cold engine is warming up. As the engine approaches normal operating temperature, the PCM leans out the fuel mixture to reduce emissions and fuel consumption. A faulty coolant sensor that always reads cold may cause the fuel control system to run rich, pollute and waste fuel. A coolant sensor that always reads hot may cause cold driveability problems such as stalling, hesitation and rough idle.
  2. Spark advance and retard. Spark advance is often limited for emission purposes until the engine reaches normal operating temperature. This also affects engine performance and fuel economy.
  3. Exhaust gas recirculation (EGR) during warm-up. The PCM will not allow the EGR valve to open until the engine has warmed up to improve driveability. If EGR is allowed while the engine is still cold, it may cause a rough idle, stalling and/or hesitation.
  4. Evaporative emissions control canister purge. Fuel vapors stored in the charcoal canister are not purged until the engine is warm to prevent driveability problems.
  5. Open/closed loop feedback control of the air/fuel mixture. The PCM may ignore the oxygen sensor rich/lean feedback signal until the coolant reaches a certain temperature. While the engine is cold, the PCM will remain in “open loop” and keep the fuel mixture rich to improve idle quality and cold driveability. If the PCM fails to go into “closed loop” once the engine is warm, the fuel mixture will be too rich causing the engine to pollute and waste gas. This condition may also lead to spark plug fouling.
  6. Idle speed during warm-up. The PCM will usually increase idle speed when a cold engine is first started to prevent stalling and improve idle quality.
  7. Transmission torque converter clutch lockup during warm-up. The PCM may not lockup up the torque converter until the engine has warmed up to improve cold driveability.
  8. Operation of the electric cooling fan. The PCM will cycle the cooling fan on and off to regulate engine cooling using input from the coolant sensor. This job is extremely important to prevent engine overheating. Note: On some vehicles, a separate coolant sensor or fan switch may be used for the cooling fan circuit only.


Most coolant sensors are “thermistors” that change resistance as the temperature of the coolant changes. Most are the “NTC” (Negative Temperature Coefficient) type where resistance drops as the temperature goes up. With this type of sensor, resistance is high when the engine is cold. As the engine warms up, the internal resistance of the sensor drops until it reaches a minimum value when the engine is at normal operating temperature.

A typical GM coolant sensor, for example, may have around 10,000 ohms resistance at 32 degrees F and drop to under 200 ohms when the engine is hot (200 degrees). A Ford coolant sensor, by comparison, may read 95,000 ohms at 32 degrees and drop to 2,300 ohms at 200 degrees.

Resistance specifications will vary depending on the application, so any sensor that does not read within its specified range should be replaced.

Coolant sensors have two wires (input and return). A 5-volt reference voltage signal is sent from the PCM to the sensor. The amount of resistance in the sensor reduces the voltage signal that then returns to the PCM. The PCM then calculates coolant temperature based on the voltage value of the return signal. This number can be displayed on a scan tool, and may also be used by the instrument panel cluster or driver information center to display the temperature reading of the coolant.

On some applications, a “dual range” coolant temperature sensor may be used. When the coolant reaches a certain temperature, the PCM changes the reference voltage to the sensor so it can read the coolant temperature with higher accuracy (higher resolution).

Older vehicles

On some older vehicles, a different type of coolant sensor may be used. Some of these are essentially an on/off switch that opens or closes at a predetermined temperature. The sensor may be wired directly to a relay to turn the electric cooling fan on and off, or it may send a signal to a warning light on the instrument panel. These older coolant sensors are typically single wire sensors. On other older applications, a single wire variable resistor temperature sensor that grounds through the threads may be used to send a temperature signal to a gauge on the instrument panel. These are typically called temperature “senders” rather than sensors.



The coolant sensor is typically located near the thermostat housing in the intake manifold. On a few vehicles, the coolant sensor may be located in the cylinder head, or there may be two coolant sensors (one for each cylinder bank in a V6 or V8 engine) or one for the PCM and a second for the cooling fan.

The sensor is positioned so the tip will be in direct contact with the coolant. This is essential to produce a reliable signal. If the coolant level is low, it may prevent the coolant sensor from reading accurately.


Because of the coolant sensor’s central role in triggering so many engine functions, a faulty sensor (or sensor circuit) will often cause cold driveability and emission problems. A bad coolant sensor can also cause a noticeable increase in fuel consumption, and it may cause a vehicle to fail an emissions test if it prevents the engine management system from going into closed loop.

Keep in mind that many coolant sensor problems are more often due to wiring faults and loose or corroded connectors than failure of the sensor itself.

Cold driveability

The coolant sensor’s impact on the engine management system, cold driveability, emissions and fuel economy can also be influenced by the thermostat. If the thermostat is stuck open, the engine will be slow to warm up and the coolant sensor will read low. Or, if someone installed the wrong thermostat for the application or removed the thermostat altogether, it will prevent the engine from reaching normal operating temperature and cause the coolant sensor to read low.

A faulty coolant sensor may also cause the engine to overheat if it fails to energize the cooling fan relay when the engine gets hot.

A faulty coolant sensor may also cause inaccurate coolant temperature gauge readings on the instrument panel.


On 1996 and newer vehicles with OBD II onboard diagnostic systems, a faulty coolant sensor may prevent some of the system monitors from running. This will prevent the vehicle from passing an OBD II emissions test because the test can’t be done unless all the required system monitors have run and passed.

The OBD II system should catch the fault, turn on the Check Engine Light or Malfunction Indicator Lamp (MIL), and set one of the following diagnostic trouble codes:

P0115….Engine Coolant Temperature Circuit
P0116….Engine Coolant Temperature Circuit Range/Performance
P0117….Engine Coolant Temperature Circuit Low Input
P0118….Engine Coolant Temperature Circuit High Input
P0119….Engine Coolant Temperature Circuit Intermittent

On older pre-OBD II vehicles, the Check Engine light may come on if the coolant sensor is shorted, open or is reading out of range. GM coolant sensor codes include codes 14 & 15, Ford codes are 21, 51 & 81, and Chrysler codes are 17 & 22.


A visual inspection of the coolant sensor will sometimes reveal a problem such as severe corrosion around the terminal, a crack in the sensor, or coolant leaks around the sensor. But in most cases, the only way to know if the coolant sensor is good or bad is to measure its resistance and voltage readings.

On vehicle systems that provide direct access to sensor data with a scan tool, the coolant sensor’s output can usually be displayed in degrees Centigrade (C) or Fahrenheit (F). The coolant sensor should read low (or ambient temperature) when the engine is cold, and high (around 200 degrees) when the engine is hot. No change in the reading or a reading that obviously does not match engine temperature would indicate a faulty sensor or a wiring problem.

Internal resistance

The internal resistance of a coolant sensor can also be checked with an ohmmeter or DVOM (digital volt ohm meter) and compared to specifications. If the sensor is open, shorted or reads out of range, it must be replaced.

If the resistance of a coolant sensor is within specifications and changes as engine temperature changes, but the engine is not going into closed loop, the fault is in the wiring or PCM. Further diagnosis will be needed to isolate the problem before any parts are replaced.

One trick here is to use a sensor simulator tool to feed a simulated temperature reading through the sensor’s wiring harness to the PCM. If the wiring continuity is good but the PCM fails to go into closed loop when you send it a “hot coolant” signal, the problem is in the PCM.



You can also use a voltmeter or digital storage oscilloscope (DSO) to check the sensor’s output. Specs vary, but generally a cold coolant sensor will read somewhere around 3 volts. As the engine warms up and reaches operating temperature, the voltage drop should gradually decrease down to about 1.2 to 0.5 volts. If you’re using a scope to display the voltage signal, you should get a trace that gradually slopes from 3 volts down to 1.2 to 0.5 volts in three to five minutes (or however long it normally takes the engine to reach normal operating temperature).

If the voltage drop across the coolant sensor reads at or near 5 volts, it means the sensor is open or it has lost its ground connection. If the voltage is close to zero, the sensor is shorted or it has lost its reference voltage.

When working on 1985 and up Chrysler products, watch out for a sudden voltage increase as the engine warms up. This is normal and is produced by a 1000 ohm resistor that switches into the coolant sensor circuit when the sensor’s voltage drops to about 1.25 volts. This causes the voltage to jump back up to about 3.7 volts, where it again continues to drop until it reaches a fully warmed up value of about 2.0 volts.

Sudden voltage changes

Sometimes a coolant sensor will suddenly go open or short when it reaches a certain temperature. If your voltmeter has a “minimum/maximum” function, you can catch sudden voltage fluctuations while the sensor is warming up. If you are viewing the voltage pattern on a scope, a short will appear as a sudden drop or dip in the trace to zero volts. An open would make the trace jump up to the VRef voltage line (5 volts).

If the coolant sensor reads normally when cold (high resistance and 3 or more volts), but never seems to reach normal temperature it could be telling the truth! An open thermostat or the wrong thermostat may be preventing the coolant from reaching its normal operating temperature.


Most coolant sensors are not replaced unless they have failed. A coolant sensor that is shorted, open or reading out of range obviously can’t provide a reliable temperature signal and must be replaced for the engine management system to function properly. But many experts also recommend installing a new coolant sensor if you are replacing or rebuilding an engine. Why? Because coolant sensors can deteriorate with age and may not read as accurately as they did when they were new. Installing a new sensor can eliminate a lot of potential problems down the road.

It is also a good idea to replace the coolant sensor and thermostat if the engine has experienced a case of severe overheating. Abnormally high engine temperatures can damage these components and may cause them to misbehave or fail prematurely.

Replacing a coolant sensor requires draining some of the coolant from the cooling system. You do not have to drain the entire radiator. Just open the drain valve and let out enough coolant so the coolant level in the engine is below the sensor.

Coolant condition check

This would be a good to check the condition of the coolant, and to replace it if the coolant is more than three years old (conventional coolant) or five years old (long life coolant). A coolant change and a flush would also be a good idea if the coolant shows any signs of contamination.

The threads on the coolant sensor may be pre-coated with sealer to prevent coolant leaks. Tighten the sensor carefully to prevent damage.

Once the new sensor has been installed, you can refill the cooling system. Make sure all the air is out of the cooling system. Air trapped under the thermostat may cause the engine to overheat or the coolant sensor to not read correctly.

Engine Air Temperature Sensor

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Engine Air Temperature Sensor

Engine Air Temperature Sensor

The Intake Air Temperature sensor (IAT) monitors the temperature of the air entering the engine. The engine computer (PCM) needs this information to estimate air density so it can balance air air/fuel mixture. Colder air is more dense than hot air, so cold air requires more fuel to maintain the same air/fuel ratio. The PCM changes the air/fuel ratio by changing the length (on time) of the injector pulses.

On pre-OBD II vehicles (1995 & older), this sensor may be called an Air Charge Temperature (ACT) sensor, a Vane Air Temperature (VAT) sensor, a Manifold Charging Temperature (MCT) sensor, a Manifold Air Temperature (MAT) sensor or a Charge Temperature Sensor (CTS).



The Intake Air Temperature sensor is usually mounted in the intake manifold so the tip will be exposed to air entering the engine. On engines that use mass airflow (MAF) sensors to monitor the volume of air entering the engine, the MAP sensor will also have an air temperature sensor built into it. Some engines may also have more than one air temperature sensor (two if it has a split intake manifold or separate intake manifolds on a V6 or V8 engine).

The air temperature sensor is a thermistor, which means its electrical resistance changes in response to changes in temperature.

It works the same as a coolant sensor. The PCM applies a reference voltage to the sensor (usually 5 volts), then looks at the voltage signal it receives back to calculate air temperature. The return voltage signal will change in proportion to changes in air temperature. Most air temperature sensors are negative temperature coefficient (NTC) thermistors with high electrical resistance when they are cold, but the resistance drops as they heat up. However, some work in the opposite manner. They are positive temperature coefficient (PTC) thermistors that have low resistance when cold, and increase in resistance as they heat up. The changing resistance of the sensor causes a change in the return voltage back to the PCM.

On older pre-OBD II applications (1995 & older vehicles), the signal from the air temperature sensor may also be used to turn on the cold start injector (if used) if the outside air temperature is cold. On some of these older applications, the air temperature sensor signal may also be used to delay

the opening of the EGR valve until the engine warms up.

Air temperature sensors are also used in Automatic Climate Control systems. One or more air temperature sensors are used to monitor the temperature of the air inside the passenger compartment, as well as the outside air temperature. The climate control system usually has its own separate outside air temperature sensor located outside the engine compartment so engine heat does not affect it. The outside air temperature sensor will usually be mounted behind the grille or in the cowl area at the base of the windshield.). Most of these sensors work exactly the same as the engine air temperature sensor. But some use an infrared sensor to monitor the body temperature of the vehicle’s occupants.


An air temperature sensor can sometimes be damaged by

backfiring in the intake manifold. Carbon and oil contamination inside the intake manifold can also coat the tip of the sensor, making it less responsive to sudden changes in air temperature. The air temperature sensor itself may also degrade as a result of heat or old age, causing it to respond more slowly or not at all.

Sensor problems can also be caused by poor electrical connections at the sensor. A loose or corroded wiring connector can affect the sensor’s output, as can damaged wiring in the circuit between the sensor and PCM.


If the intake air temperature sensor is not reading accurately, the PCM may think the air is warmer or colder than it actually is, causing it to miscalculate the air/fuel mixture. The result may be a lean or rich fuel mixture that causes driveability symptoms such as poor idle quality when cold, stumble on cold acceleration, and surging when the engine is warm.

If the engine computer uses the air temperature sensor input to turn on a cold start injector, and the sensor is not reading accurately, it may prevent the cold start injector from working causing a hard cold start condition.

A faulty air temperature sensor may also affect the operation of the EGR valve is the PCM uses air temperature to determine when the EGR valve opens (on most, it uses the coolant temperature input).

On OBD II application (1996 & newer vehicles), a faulty air temperature sensor may prevent the Evaporative (EVAP) Emissions System Monitor from completing. This can prevent a vehicle from passing a plug-in OBD II test (because all the OBD II monitors must run before it can pass the test). The EVAP monitor will only run when the outside temperature is within a certain range (not too cold and not too hot, as a rule).

A faulty air temperature sensor that is reading warmer than normal will typically cause in a lean fuel condition. This increases the risk of detonation and lean misfire (which hurts fuel economy and increases emissions).

A faulty air temperature sensor that is reading colder than normal will typically cause a rich fuel condition. This wastes fuel and also increases emissions.

Sometimes what appears to be a fuel mixture balance problem

due to a faulty air temperature sensor is actually due to

something else, like an engine vacuum leak or even a restricted catalytic converter! A severe exhaust restriction will reduce intake vacuum and airflow causing the sensor to read hotter than normal (because it is picking up heat from the engine).



A faulty air temperature sensor may or may not set a code and turn on the Check Engine light. If the sensor circuit is open or shorted, it will usually set a code. But if it is only reading high or low, or is sluggish due to old age or contamination, it usually will not set a code.

A quick way to check the air temperature sensor is to use a scan tool to compare the air temperature reading to the coolant temperature reading once the engine is warm. A good air temperature sensor will usually read a few degrees cooler

than the coolant sensor.

The sensor’s resistance can also be checked with an ohmmeter.

Remove the sensor, then connect the two leads on the ohmmeter to the two pins in or on the sensor’s wiring connector plug to measure the sensor’s resistance. Measure the sensor’s resistance when it is cold. Then blow hot air at the tip of the sensor with a blow drier (never use a propane torch!) and measure the resistance again. Look for a change in the resistance reading as the sensor warms up.

No change in the sensor’s resistance reading as it heats up would tell you the sensor is bad and needs to be replaced. The sensor reading should gradually decrease if the sensor is a negative thermistor, or gradully increase if it is a positive thermistor. If the reading suddenly goes open (infinite resistance) or shorts out (little or no resistance), you have a bad sensor.

To be really accurate, you should look up the resistance specifications for the air temperature sensor, then measure the sensor’s resistance at low, mid-range and high temperatures to see if it matches the specifications. A sensor that reads within the specified range when cold, may go out of range at higher temperature, or vice versa. Such a sensor would not be accurate and should be replaced.

The resistance and/or voltage test specifications for the air temperature sensor on your engine can be found in a service manual, or by subscribing to the service information on the (Vehicle Mfrs Service Information Website or AlldataDIY.



The air temperature sensor is a solid state device so no adjustment is possible. However, it may be possible to clean a dirty sensor so that it functions normally once again provided it is still in good working condition. Contaminants can be removed from the tip of the sensor by (1) removing the sensor from the intake manifold, then (2) spraying the sensor tip with electronics cleaner. For sensors that are mounted inside a MAF sensor, the wire sensing element can also be sprayed with aerosol electronics cleaner. Do not use any other type of cleaner as it may damage the plastic housing or leave behind a chemical residue that may cause problems down the road.

If a sensor is not reading within specifications or has failed, replace it. Fortunately, most air temperature are not very expensive (typically less than $30). Dealers always charge more than aftermarket auto parts stores, so shop around and compare prices before you buy. Labor to change an air temperature sensor is usually minimal, unless the sensor is buried under a lot of other stuff that has to be removed.

When replacing the air temperature sensor, be careful not to overtighten it as this may damage the sensor housing, or the threads in a plastic intake manifold.