Mass Airflow Sensors
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 SENSOR OUTPUT
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
MASS AIRFLOW SENSOR DIAGNOSTIC FAULT CODES
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.
MASS AIRFLOW SENSOR DIAGNOSIS
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.
CLEANING FORD MAF SENSORS
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 (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: 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.
The engine coolant temperature (ECT) Sensor
HOW THE COOLANT SENSOR AFFECTS ENGINE OPERATION
TYPES OF COOLANT SENSORS
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:
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.
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).
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.
COOLANT SENSOR LOCATION
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.
COOLANT SENSOR SYMPTOMS
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.
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.
COOLANT SENSOR DIAGNOSTIC FAULT CODES
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.
COOLANT SENSOR DIAGNOSIS
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.
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.
COOLANT SENSOR VOLTAGE CHECKS
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.
COOLANT SENSOR REPLACEMENT
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
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).
HOW THE AIR TEMPERATURE SENSOR WORKS
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).
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.
CAUSES OF FAILURE
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).
DIAGNOSING THE AIR TEMPERATURE SENSOR
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.
AIR TEMERATURE SENSOR REPLACEMENT/REPAIR/ADJUSTMENT
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 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.
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.
O2 SENSOR HEATER CIRCUIT
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
Improved Mosfet switching circuit for powering Hydrogen fuel system
MOSFET switch for hydrogen generator systems
A Simple Switch
MOSFETs are really easy to “saturate”, which just means that they are fully open, and they are dead reliable for very fast switching between their saturation and cut-off regions (fully on and fully off regions). This makes them wonderful switches, especially for high power applications like motors, lamps, etc. In most cases, you can use the same power supply that you are using for your high power device to operate the MOSFET as well, using a mechanical switch to apply the gate voltage. The image below shows exactly that type of application
For this project wewill use N channel MOSFET only
Place the N-ch MOSFET on the board. Connect the 1kΩ resistor between the gate and GND. Connect the switch between the gate and +9V. Place the 220Ω resistor and LED in series between +9V and the drain. Tie the source pin directly to GND. See image below.
Push the button and the LED should light up. The 1kΩ resistor acts as a pull-down resistor, keeping the voltage at the gate at the same potential as the negative battery terminal until the button is pushed. This puts a positive voltage at the gate, opening the channel between the drain and source pins and allowing current to flow through the LED. Note that the gate voltage is +9V and there are no negative side effects.
Step 3: Motor Drivers – not applicable or necessary configuration for Hydrogen electrolysis circuits
Improved Mosfet switching circuit
Building off of Step 1, we can use the ZVN as a DC motor driver. To avoid over-current damage to the ZVN, I’m using a small 6V DC hobby motor, much like the kind you find inside of small hobby servos. With a higher current N-ch MOSFET, you can drive larger motors with larger current needs.
Looking at the schematic below you’ll see two diodes placed backward (reverse biased) across the motor contacts and across the MOSFET drain/source pins. Any electrical component that has a coil in it (inductors, relays, solenoids, motors, etc.) can generate a very large voltage spike in the reverse direction when it is turned off. (This is a common problem in airsoft, and it can lead to premature wear on the trigger contacts that turn on the motor. An easy fix for this is to add an “airsoft MOSFET”, and this is a similar example. It should be noted that the parts used here are nowhere near capable of handling the voltage/current needs of an airsoft motor, so don’t use this specific example.) The diodes give that spike a place to go so that the components are not damaged.
Improved Mosfet switching circuit
Build: Place the ZVN on the board. Connect the 1kΩ resistor between the gate and GND. Connect the switch between +6V and the gate. Connect the source to GND. Connect the drain to the negative motor lead. Tie the positive motor lead to +6V. Place one diode between the drain and source pins, with the stripe on the diode facing the drain pin. Put the other diode across the motor leads, with the stripe toward +6V. See image below.
Once everything is connected, double check it. And again. It’s really easy to get things switched and even though it probably won’t matter with this circuit, it’s a good habit to already have when it does matter. Then push the button and your motor should run in one direction.
Improved Mosfet switching circuit
As you can see MOSFETs are extremely useful. They are arguably the most important electronic component in use today when you look at how much we rely on them for our everyday electronic devices. There isn’t a day that goes by that you don’t use several million transistors just to do something simple, like look at what time it is. Or make your coffee, check your email, watch a movie, listen to music, or read this I’ble.
You may have noticed that there is no mention of MOSFETs as amplifiers here. I did that on purpose, but that isn’t to say that they can’t be used as such. My experience has been that analog signal amplification duties are best handled by BJTs, and fast, high current switching is best done by MOSFETs. I realize that is a generalization, as there are plenty of examples for both transistor types working both ways very well. I encourage you to do the research yourself if you wish to learn more on those applications.
Improved power supplies
Have been doing a many hours R and D on development of a new improved power supply for hydrogen fuels systems. The Issue I have experienced is the excessive wastage of electrical energy in operating a power supply originally designed to power DC motors , that have an excessive amount of electrical circuitry whose only function is to prevent back voltage that reduces the efficiency and Power output of an inductive DC motor circuit.
Improved power supplies
There are many potential sites available online , both on you tube and on research URL sites that describe effective DC control / switching circuits that use MOSFET components . Many of these are still biased to DC motor circuits but we have managed to modify several simple circuits that use Banks of MOSFET’s connected in parallel with biasing 10k pots , to control / switch the current on in these Electrolysis circuits , without wasting excessive voltage on the internal circuitry.
After many many many hours of operation and testing of these switching Power supply circuits we will now get them made professionally and install them in the latest models of hydrogen fuel systems.
There are several advantages of the new circuitry
- All available battery voltage / electrical energy is available for the electrolysis cells
- No overvoltage is wqsted through the PWM heat sink , thus preventing problem s of electronic thermal runaway problem
- The MOSFET is a VOLTAGE CONTROLLED DEVICE rather than a current controlled device as in transistors ad IC’s thus leaving little chance of thermal runaway damage and making it easier to set, control and use
- Less parts , simpler construction and less maintenance problems
- Truly able to use as a set and forget technology
- Cheaper to manufacture and cheaper to repair if so needed
Improved power supplies
Recommended Mosfets for these systems are the 10 amp 12 volt MOSFETS, – 5 OF THEM CONNECTED IN PARALLEL. Providing control for up to 50 amp of current .
Once the systems are manufactured professionally by our fabricator, they will be mounted into a protective ventilated cage onto a designed circuitboard
Photos will follow soon and schematics will be available on this site
“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.”
hydrogen–diesel duel fuel testing at University of Tasmania 2006
As Part of this website , and with being a Qualified Astro-Physicist, Chemist and Civil Engineer , I have decided to publish a series of interactive PDF documents with the aim of educating our young girls and boys interested in studying Physics and Chemistry.
INITIALLY these documents / posts will be mixed in with the hydrogen fuel systems posts. The aim of these posts is to help my year 12 Physics students working on Particle-physics and the structure of matter — Australian Science Curriculum
M9re to follow