I like to write about automotive topics—particularly DIY stuff and auto concepts.
The engine control module (ECM) is also known as the powertrain control module (PCM) or the engine control unit (ECU).
The main responsibility of this controller is to get information from sensors and run certain actuators. In the case of any errors, the ECU shows a check engine light on your dashboard.
We will discuss where and why sensors are placed in certain positions and give some insight as to how or what the sensors sense. If you are a DIY person, then you could even open up the sensors yourself and clean them for optimum signals to reach your ECU.
Engine Control Module
No matter how complicated, you'll find the sensors below in any EFI engine:
- Engine coolant temperature
- Air temperature
- Barometric pressure/manifold absolute pressure
- Mass air flow
- Idle air controller
- Throttle position
Engine Coolant Temperature Sensor (ECT)
Like humans, a vehicle needs to maintain a specific temperature in order to function properly. Too cold, and the vehicle will drink too much petrol. Too hot and the head gasket could leak. Coolant is a liquid used in the vehicles radiator of the car to maintain the temperature at which the engine can perform at its optimum.
The engine coolant temperature sensor simply tells the car's computer (ECM) the current temperature of the vehicle. When the temperature of the coolant reaches between 75 and 95 degrees (depending on the manufacturer specifications), the ECM instructs the radiator fan to turn on and start cooling down the liquid.
- Usually it is located either on the bottom of the radiator, or by follow the top radiator hose towards the engine block. You'll see it on mounted on the engine block.
- It can be cleaned using a wire brush when you entirely change your engine coolant (approx. every 80,000 km or 50,000 miles).
Air Temperature Sensor (IAT)
The intake air temperature sensor (IAT) tells the ECM the temperature of the air that is going into the engine. The cooler the air, the better the performance of the engine, which is probably why you might have noticed a difference in the car's performance on a summer night as compared to the day.
- It is usually located on the air filter box or the pipe going from the air filter box to the throttle body. Toyota has a MAF and an IAT sensor built in one unit which has five wires located on the air filter box.
- It can be cleaned once every six months (depending on dust/pollution), using carb cleaner on an ear cleaner.
BARO/Manifold Absolute Pressure Sensor (MAP)
The baro sensor measures the ambient air pressure, which tells the ECM the current altitude of the vehicle. If you're driving in the mountains you'll need less fuel, because there is less oxygen in the atmosphere and therefore less oxygen in the engine cylinder. The ECM will adjust the fuel injectors "throwing time" or pulse width accordingly.
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The map sensor detects the vacuum pressure created inside the intake manifold of the vehicle and sends the engine load information to the ECM. The ECM will adjust the fuel injectors pulse width accordingly.
Note: Baro and MAP sensors look and work in a similar fashion, therefore only one of the two sensors will be found in one engine.
- Usually found either bolted on the intake manifold or linked with a vacuum pipe from the intake manifold.
- If mounted on intake manifold then should be cleaned every 6 months to 1 year, using carb cleaner (depends on fuel quality where you live; the lower the quality of fuel, the more carbon deposits found). I've had to clean some every three months.
Mass Air Flow Sensor
The Mass Air Flow sensor is responsible for measuring the volume of air entering the engine.
The sensor contains a heated sensing element, as shown in the picture above. The temperature of this element has to be kept constant, but is cooled by the air passing through the intake. The MAF sensor produces more current to keep the temperature at the level required by the manufacturer. There is a small computer in the MAF which calculates the internal current flow to heat the element, and by using this figure it can calculate the volume of air going into the engine as well as the air density and temperature. The ECU uses this information to adjust the injector pulse width and spark (ignition) timing.
- The MAF Sensor is located either on the air cleaner box or along the pipe going from the air cleaner to the throttle body.
- Note: Since the MAF sensor calculates the air density, the engine does not need the MAP or baro sensor readings. Therefore you will not see a MAP or baro sensor in your engine if you have a MAF installed and vice versa.
- Can be cleaned with carb cleaner or MAF cleaner spray and ear cleaning bud. Clean if you see dust or carbon deposits.
Idle Air Controller (IACV)
The Idle Air Control Valve (IACV) is responsible for keeping the RPM of the engine steady. The IACV is actually an actuator and not a sensor because it does not supply readings to the ECM, but works on the command of the ECM. I just added this actuator for the DIY enthusiast.
There are two coolant pipes connected to the housing, which you can see on the far right of the picture shown. The black piece shown in the picture is a magnetic actuator which rotates the valve shaft allowing it to open and close as required by the ECM.
Whenever you start your car the IACV will increase the RPM until the coolant temperature sensor (ECT) tells the ECU that the temperature of the engine is up-to the manufacturers specifications. The RPM will then drop down to and remain steady at approx 800 rpm whenever there is an extra load on the engine the idle controller adjusts and compensates for the load applied—for example, switching from park to drive mode in an automatic transmission vehicle, or even when you switch on your air conditioning. You can also adjust the idle speed of the vehicle by loosening the screws on the actuator and rotate the actuator. The default setting of the actuator is normally in the middle.
- Located on the throttle body of the vehicle.
- Depending on fuel quality, carbon deposits build up and the valve shaft gets stuck resulting in fluctuating RPM signals on the dashboard.
- To clean remove the black magnetic actuator which will reveal the shaft. Try rotating the shaft with your fingers. If it's a little hard, then use carburetor cleaner and a toothbrush or ear cleaning bud to clean the area of the valve (the two identical rectangular blocks), and check to see if the shaft is easy to rotate. When putting the magnetic sensor back, make sure the rubber O-ring goes on the metal housing and then align the tip of the shaft with the step inside the magnetic sensor. Set the sensor to the mid-position and tighten the screws.
- Note: On some vehicles a scanner is required to reset the idle controller once opened.
Throttle Position Sensor (TPS)
The throttle position sensor (TPS) is linked from the accelerator pedal to the throttle body.
The TPS tells the ECM that the driver is pressing the accelerator pedal. The ECM can also verify this information with the MAP or MAF sensor readings, thus increasing the injector pulse width and spark (ignition) timing.
- The TPS is located on the throttle body. Honda has an adjustable TPS sensor and if the initial if your RPM is high and cannot be controlled through the IACV, then the voltage readings of the TPS should be checked. The normal reading for a Honda is close to 0.6V at idle.
I remember playing with the TPS in my friend's car and adjusting his TPS to about 2.5 volts at idle. The result: The became a gas guzzler, consuming about 30 litres of petrol (about 7 gallons) in 30 km (about 18 miles). I guess we learned the hard way.
A newer system for the throttle control came in 2003-2005 and newer models of vehicles, in which a throttle cable is no longer used. A sensor has been placed in the accelerator pedal and the TPS sensor has been replaced with a throttle position motor.
- This sensor never requires cleaning. If you do want to clean something on it then just clean the connector points with electrical contact cleaner and a toothbrush. That goes for all the sensors.
Camshaft Position Sensor
The camshaft position sensor (CMP) is electro-magnetic and produces a voltage when a metal object moves past. This sensor is responsible for telling the ECM the current position of the camshaft. With this information the ECM can calculate which valve is open and throw fuel through the injector into that cylinder.
- This sensor is found on one end of the camshaft, usually on the right side in a front wheel drive car. It's normally not very difficult to access.
- Cleaning can be done with a simple dry cloth, but if the oil has been used for too long, a golden-brown stain is left on metal portion of the sensor. In some cases it even comes out black and gooey, which is basically old engine oil turned into sludge. if it's stained then you can use a wire-brush or very fine sandpaper to remove the stain. Make sure no metal bits remain on the sensor. If you need some liquid type material to get some stains off, try WD-40.
Crankshaft Sensor (CKP)
This sensor is very similar to the cam position sensor in functionality. It is responsible for telling the ECM the exact location of the crankshaft as well as the RPM (rotations per minute) of the engine. With this information the ECM knows the position of each piston in each cylinder. Using the cam sensor readings, as well as the crank sensor readings, the ECM knows exactly which injector needs to be activated. The synchronization of the cam and crank shafts in an engine is the key to engine performance. This synchronization is also referred to as the engine timing. With the correct timing you will get the fuel and spark delivered at the right time.
- It is located at the bottom of the engine somewhere close to the crankshaft.
- Cleaning technique for this sensor is exactly the same as the cam sensor. Cleaning once a year is good enough for this sensor.
- Note: If your car does not start, a possible reason could be a faulty crank sensor or a broken wire in the crank sensor circuit.
Oxygen Sensor (O2)
The oxygen sensor (O2) is responsible for "smelling" the exhaust fumes and detecting the oxygen content in order to make sure the engine is consuming the right amount of fuel. The ratio maintained by the ECM is 14.7 parts air to 1 part fuel. This is known as the air/fuel ratio.
There are two types of oxygen sensor: zirconia or titania. These are materials which can detect oxygen and produce a voltage. The voltage range falls between 0.1V to 0.9V.
I normally use a vehicle scanner to check the maximum and minimum readings of the oxygen sensor. If I see both peaks, then I know the sensor is working fine. If the voltage max is 0.8 then I open up the sensor for cleaning. Sometimes the sensor produces a constant voltage but does not fluctuate. This generally means the sensor needs to be replaced.
The knock sensor contains a piezoelectric crystal. This crystal is able to detect mechanical stress and produces a voltage when the car knocks or pings. Under heavy acceleration, it sends signals to the ECM and the ECM retards the ignition timing to compensate for the knocking, which in effect protects the pistons and rings from damage.
Knocking also occurs when using low-grade fuel and having the knock sensor allows you to use different grade fuels without causing engine damage.
- This sensor is normally bolted onto the main-body of the engine in the most difficult and awkward positions. Lucky this sensor never requires cleaning.
What Happens If One of These Sensors Fail?
If a sensor fails and gives abnormal readings, for example a coolant temperature sensor giving a constant reading of -40o, then the ECM goes into fail-safe mode. This means it basically ignores the values of the sensor at fault and tries to either calculate the value of the failed sensor or assumes a constant reading so the vehicle can keep running. Some faliures like a crank sensor or a MAF sensor will result in the vehicle not starting at all.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: What allows for an engine to be diagnosed?
Answer: Any malfunction in the sensors or mechanical issues.
Question: After cleaning my 1999 Honda Accord 4 cylinder 2.3 l VTEC all the carbon out of the intake system. My car starts to run, then stalls out and will not start back up. What's the problem and what should I check?
Answer: Check MAF / MAP sensor electrical grip (whichever your car has) and look for air leaks.
Question: I am in the UK and have a Seat Leon with 1.4tsi 150bhp. If I drive off in the morning, the engine warning light comes on after about 5 mins. The code reader shows fault code PO11F re ECT sensor. Can this be erased & not come back until next day? The car otherwise runs fine. If I start and then stop before driving off in the morning, the warning light does not come on at all. I'm wondering if the fault could be related to an ECU remap I did. Firm that did the remap is adamant that the fault isn't related. Is that true?
Answer: PO11F In most cases seems to point toward emissions rather than the ECT. Even though the vehicle shows and ECT error there is an underlying problem which will not fix the problem even if you change sensors. I would say first, check the fuel pump pressure when you turn they key in the ON position (priming; without starting the engine). Second; check if your Catalytic converter is choked (if you have problems with fuel consumption). In another source, the code given is associated with overheating and a blown head gasket or even a minor timing belt issue. It could be one of these but cannot be confirmed as I’m not entirely sure what the remap includes. Try to eliminate the easier ones to see if it works. If the easy ones don’t do it then wait until the light stays on longer and comes on more often to check the rest.
Question: Is the controller for the heater on an O2 sensor in the ECM?
Answer: Heater location is inside the O2 sensor. Heater is controlled by the ECM so there would be a chip on the ECM board that would control the O2.
Question: My 2010 Ford Mustang 4.0 is hiccuping, jerking, and it feels like it’s hesitating to accelerate. When I’m making a complete stop the car will shut itself off. Why is this the case?
Answer: Look for air leaks in the intake area.
Question: My Nissan sunny 2004 model cranks but does not pick up and the injectors do not spray fuel. What can I do?
Answer: Change CAM sensor and try.
Question: Can my 2000 Toyota car without a camshaft sensor make itself consume fuel? Can I clean the exhaust sensor to make it work again?
Answer: If the exhaust sensor is dead it will not work again. If the readings are not in the correct range then cleaning can improve it. Excessive fuel consumption is only if the MAP sensor has stopped working. You will see black smoke come out of the exhaust if that is the case. If that is not happening then your fuel filter could be choked and needs replacing or valve clearances need to be checked especially on the exhaust side.
Question: My car is mark 2 2.0cc .2002 model. When I start it, I notice a smell of fuel and the fuel consumption is a little high. What can I do?
Answer: Check for leaks in fuel rail
Question: Can you tell me where the ECM is on a 1984 Pontiac 6000?
Answer: Not exactly sure. Some sources say in the air filter box in the engine bay and others say in the dashboard. You could follow the sensor wiring loom to get to the PCM.
Question: how can I tell if the knock sensor is faulty?
Answer: You will get a check engine light which will indicate it is faulty. If there is no indication then it is fine and the problem is somewhere else. If still in doubt then replace it.
Question: My Cadillac cts 05 has a code reading u0100 and check engine light and will not go over 2rpm would like to know what's wrong?
Answer: A bit of a serious issue with either the wiring or the control module. The ECM cannot pick up signals from either the engine or the transmission modules.
A rat could have eaten up the wires or the connections may be loose. You will have to trip the carpet and follow the wiring to make sure it’s all good. If all good then try changing the controller units. Continuity test between the cables to find faulty cables. The problem lies in the main network of cabling; not the sensors. It will continue to stay in limp mode (2mph) until the issue is fixed.
Question: Is a sensor & module for the transmission considered the same part?
Answer: No. A module is a separate ECU that controls the transmission. Sensors give the module information. Have a look at the transmission control module article I have written to get more info on the types of sensors used with the transmission control module.
Question: We had some trouble codes leading us to fix our TPS and IACV but we still have black smoke and high idling and occasionally stalls. No trouble codes now, any idea which direction to take?
Answer: Confirm the TPS is installed properly. Sometimes it does not rotate if in the wrong position. With the ignition on press, the accelerator pedal and either use a multimeter on the sensor wires or using a scanner make sure the voltage is approx 0.6v with nothing pressed then press the accelerator pedal to “wide open throttle” position. At wide open throttle, it should be approximately 4.5volts. If these are correct then Make sure IACV is set to the middle point of the 2 screws making sure there are no air leaks in the throttle area. You can use some silicone to ensure that.
Some vehicles (like Chevrolet) require a throttle reset through a scanner. It will never run properly until you reset using the scanner. Taking the battery terminals doesn’t work either.
If everything is good and still have black smoke then try replacing MAP/MAF sensor. that should cover it. If problems persist then send me an email with a snapshot of diagnostic voltages at idle (running engine) and another snapshot after quick heavy revs... it gives the max and minimum of each sensor which is what I would like to look at.
Question: My Toyota Camry's (2004) temp gauge always go halfway and never go higher even my Cooling fan failed. So I test my coolant sensor by an Ohm meter and the sensor terminal Voltage by Voltmeter and the reading is ok. Is there a possibility that the ECM reading is offset and need to be calibrated?
Answer: If the reading is ok then keep using it. The Camry has a large radiator which allows for natural cooling; this is why the fan doesn’t always go on.
If your water levels are stable in the cooling system then I would suggest leaving it as it is.
Question: If my temperature gauge is not working at all does this mean all the sensors have problems?
Answer: If the temperature gauge or any sensor fails you will get a check engine light. When this happens the car uses default values set by the manufacturer.
Question: 1999 Vauxhall Corsa 1.2 16v not revving past 3000 rpm, Sounds like it's revving of the limiter, but only at 3000rpms, what could cause this?
Answer: Sounds like the ECU is keeping the car in limp (safety) mode. You need to check with a scanner to see what could be causing it. Sometimes it’s the oxygen sensor, other times it could be the injectors.
Question: What would keep the check engine from coming on in a 97 Dodge 5.9?
Answer: It could be anything; you will need to get it scanned to get the code.
Question: Other than engine sensor signals, name three other inputs signals an engine control module might receive?
Answer: Turbo, Evaporative emissions control, vtec solenoid, oil control valve.
Question: My land cruiser shows a code 1421 with autel (master cylinder scan, cylinder pressure sensor). Where is the location of this sensor?
Answer: On the brake master cylinder. Look for grips near the brake fluid reservoir. It could be a broken wire, or the grip may not be on properly. If everything seems ok then try replacing the sensor.
Question: My Toyota Auris Rx 1.8 2009 model cooling fan or thermal switch does not run whenever my engine is on and even when I drive but my temperature never overheated why is this?
Answer: The cooling fan works with the thermal switch. The thermal switch will have a certain point (I.e.93 degrees Celsius) at which it will enable the current to the cooling fan. Your vehicle also has a thermostat valve which allows for the rotation of coolant within the engine. This valve also has a set temperature at which it will open to allow the cold coolant to enter the engine.
Now if you have a thermal switch which is set to run when the coolant reaches 93 degrees and also have a thermostat valve that allows for the rotation of coolant at approximately 87 degrees then the vehicle does not need the fan. It will only engage in very hot weather where the radiator cannot cool the contents (coolant) quick enough.
Question: How should I troubleshoot a changing sound from the mainfold and a bad sound on the top?
Answer: Check for air leaks.
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