Engine Control Module and Sensor Locations
The Engine Control Module (ECM) is also known as the Powertrain Control Module (PCM) or the Engine Control Unit (ECU).
The main responsiblity 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.
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 Fails?
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.