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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.

Wideband O2 Sensors and Air/Fuel (A/F) Sensors

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Wideband Oxygen sensors (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 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 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.

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 i9e8188db74cc41da7fa9c8a38232b9a2 voltage) if the air/fuel mixture is lean, or a drop in voltage (below the reference voltage) if the mixture is rich.

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

Hydrogen Fuel Conversion and University research reports

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“Just 20% of hydrogen mixed with normal diesel fuel will instantly reduce emissions by a whopping 40%. Dr Vishy Karri at the University of Tasmania is working on this technology as an add-on to existing vehicles – starting with a postie’s bike.”


hydrogendiesel duel fuel testing at University of Tasmania 2006


Hydrogen systems for Diesel Engines University Research

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Hydrogen fuel systems

Hydrogen systems for Diesel Engines University Research

Hydrogen fuel systems. Today October 3 2017, On Holidays at Ramada resort, Dunsborough WA,  I was conducting research online for the following research topic

“hydrogen systems for diesel engines university research”

I was able to find many authentic research articles including ones from a group from with URL address

Science direct is a University research URL requiring membership.,  However there are many reference links showing authors and published papers which can be easily located online through a google search

One such paper I found to start with was headed “Combustion characteristics of diesel-hydrogen dual fuel engine at low load” and was located at the URL1-s2.0-S1876610213000040-main hydrogen dual fuel

1-s2.0-S1876610213000040-main hydrogen dual fuel

Which I downloaded and have copied onto this post

The research report was well written and a clear concise document providing proof of the use of Hydrogen as a duel fuel for use with diesel

Hydrogen fuel systems

“In the present study, hydrogen utilization as diesel engine fuel at low load operation was investigated. Hydrogen cannot be used directly in a diesel engine due to its auto ignition temperature higher than that of diesel fuel. One alternative method is to use hydrogen in enrichment or induction. To investigate the combustion characteristics of this dual fuel engine, a single cylinder diesel research engine was converted to utilize hydrogen as fuel. Hydrogen was introduced to the intake manifold using a mixer before entering the combustion chamber. The engine was run at a constant speed of 2000 rpm and 10 Nm load. Hydrogen was introduced at the flow rate of 21.4, 36.2, and 49.6 liter/minute. Specific energy consumption, indicated efficiency, and cylinder pressure were investigated. At this low load, the hydrogen enrichment reduced the cylinder peak pressure and the engine efficiency.”

Hydrogen fuel systems

“The advantages of using hydrogen as fuel for internal combustion engine is among other a long-term renewable and less polluting fuel, non-toxic, odorless, and has wide range flammability. Other hydrogen properties that would be a challenge to solve when using it for internal combustion engine fuel, i.e.: low ignition energy, small quenching distance, and low density”

Hydrogen fuel systems

“5. Conclusion Experiments and simulation works were conducted on DI diesel engine with hydrogen in the dual fuel mode. Under constant load and speed engine operation, hydrogen induction into the intake manifold 10 W.B. Santoso et al. / Energy Procedia 32 ( 2013 ) 3 – 10 reduces the diesel fuel consumption. Diesel reduction of 50, 90, and 97% was achieved during the investigation. These relatively high percentages of hydrogen fuel are detrimental to the engine performance in terms of energy consumption and efficiency. An increasing hydrogen flow rate at the low load operation results in a higher SEC. It means that more fuel is necessary to produce the same power output. At this low load operation, the efficiency decreases with hydrogen enrichment. This condition affects the values of SEC. Measurement of in-cylinder pressure was carried out to investigate the combustion process inside the combustion chamber. Hydrogen enrichment reduced the peak pressure and retarded the start of combustion. CFD simulation reveals that hydrogen enrichment in such a high percentage resulted in slower reaction progress due to lower combustion rate of reaction. Temperature distributions along the cut plane at the spray axis showed the progress of the combustion processes. Acknowledgment The authors wish to thank Universiti Malaysia Pahang for supporting this research under GRS 100303. Fully support from LIPI by providing the experiment and simulation facilities are grateful acknowledged.

References [1] Fulton J, Lynch F, Marmora R. Hydrogen for reducing emissions from alternative fuel vehicle. SAE Technical Paper 1993;No. 931813.

[2] Saravanan N, Nagarajan G. An experimental investigation of hydrogen-enriched air induction in a diesel engine system. Int J Hydrogen Energy. 2008; 33:1769-1775

. [3] Pundir BP, Kumar R. Combustion and smoke emission studies on a hydrogen fuel supplemented DI diesel engine. SAE Technical Paper. 2007;No. 2007-01-0055.

[4] Saravanan N, Nagarajan G, Kalaiselvan KM, Dhanasekaran C. An experimental investigation on hydrogen as a dual fuel for diesel engine system with exhaust gas recirculation technique. Renewable Energy. 2008;33:422-427.

[5] McWilliam L, Megaritis T, Zhao H. Experimental investigation of the effects of combined hydrogen and diesel combustion on the emissions of a HSDI diesel engine. SAE Technical Paper. 2008;No. 2008-01-1787.

[6] Saravanan N, Nagarajan G, Dhanasekaran C, Kalaiselvan KM. Experimental investigation of hydrogen port fuel injection in DI diesel engine. Int J Hydrogen Energy. 2007;32:4071-4080.

[7] Lilik GK, Zhang H, Herreros JM, Haworth DC, Boehman AL. Hydrogen assisted diesel combustion. Int J Hydrogen Energy. 2010;35:4382-4398.

[8] Saravanan N, Nagarajan G, Dhanasekaran C, Kalaiselvan KM. Experimental investigation of hydrogen fuel injection in DI dual fuel diesel engine. SAE Technical Paper. 2007;No. 2007-01-1465.

[9] Saravanan N, Nagarajan G. An experimental investigation on a diesel engine with hydrogen fuel injection in intake manifold. SAE Technical Paper. 2008;No. 2008-01-1784.

[10] Saravanan N, Nagarajan G. Performance and emission studies on port injection of hydrogen with varied flow rates with Diesel as an ignition source. Applied Energy. 2010;87:2218-2229.

[11] Bose PK, Maji D. An experimental investigation on engine performance and emissions of a single cylinder diesel engine using hydrogen as inducted fuel and diesel as injected fuel with exhaust gas recirculation. Int J Hydrogen Energy. 2009;34:4847- 4854.

[12] Szwaja S, Grab-Rogalinski K. Hydrogen combustion in a compression ignition diesel engine. Int J Hydrogen Energy. 2009;34:4413-4421

Proto-typing designs

hydrogen fuel systems for cars, Uncategorized

3D printer

Recently I purchased a 3D printer with then aim of making and testing new designs in both hydrogen generator systems as well as In magnetic generators

After copying a number of designs for system modifictions finally found a program called which enabled me to quickly  create , modify , adjust , print and test a number of plastic units to be used in systems.

The Beauty of this program is that is able accurately and cheaply manufacture multiple versions of a system component without the high cost of a CNC machine

3D printer

Also provided with this program is an excellent set of training videos to teach you how to get the best of the 3D printer

These devices were used to 3d print scaled versions of both plastic and metal parts for construction of the hydrogen generator system as well as the magnetic motor system.

3D printer

I will be sharing some of these designs for the world to  view , , use, modify as required in building the new generator systems.


New Hydrogen systems installed Coogee chemicals heavy haulage trucks

hydrogen fuel systems for cars, Uncategorized

New Hydrogen systems installed Coogee chemicals

New Hydrogen systems installed  Coogee chemicals heavy haulage trucks

Pictures attached

improvement in fuel economy 20%— 16 Litre cummins diesel engine 600 HP   – new engine

Turning CO2 into Fuel Using Hydrogen generated by HFS innovative technology

hydrogen fuel systems for cars, Uncategorized

CO2 Fuel  .   An interesting report today was published by the CSIRO concerning the use of hydrogen in producing methane gas  for coal fired power stations , as a means of recycling carbon dioxide, reducing the carbon dioxide output and effectively increasing the efficiency of the Coal fired Power station and reducing carbon dioxide pollution.

Turning CO2 into Fuel – CSIRO blog

Turning CO2 into Fuel


It’s a interesting report ,especially as I have a prototype unit operational for use on coal fired power station in Australia’s East Coast.  You can imagine how I felt when I read the headline explaining how this is a new innovative proposal after I submitted my unit back in july 2016.

The major advantage of this system of H.F.S. pty ltd is that is uses the high temperature and thermal energy of the carbon dioxide to power the catalytic reaction involving hydrogen and carbon dioxide to generate Methane gas that is fed back into the power station fuel source  increase the efficiency of the system and require less coal in the first place to provide the required station power output.

The heart of the process is the patented catalyst used to combine Hydrogen and carbon dioxide together to manufacture methane. along with HFS extremely efficient Hydrogen generator technology.

This process  does not eliminate the carbon dioxide output but significantly reduces its annual output and influence on the environment.  Currently we are testing several mechanisms which effectively lock up the output gases which are not used in generating methane gas.

More INFORMATION will follow.