ECM Sensors

Location:

Varies, usually found towards the bottom of the block either near the timing cover or transmission bell

Function:

Reads the position and speed of the crankshaft, determines engine RPM

Description:

The crankshaft position sensor allows the ECM to know what the crankshaft position is, therefore knowing where each of the pistons are. The ECM uses this information to determine proper fuel injection and ignition timing. In addition to this, the ECM also uses input from the camshaft position sensor to verify that timing between the crankshaft and camshafts is accurate. Lastly, the ECM uses this sensor to measure the revolutions per minute (RPM) of the engine to pass along to the tachometer gauge.

The CKP sensor is a Hall-effect sensor, meaning it monitors magnetic fields. This sensor is always located close to the timing gear, flywheel, or another toothed-gear located on the crankshaft. As the gear spins, the head of the sensor faces the teeth and reads the pattern as they rotate. The CKP sensor will pulse volts of electricity with each tooth that passes.

The key to this system is that the gear its facing has one tooth missing around the edge. As this passes the CKP sensor, it skips an electrical pulse, and this is what lets the ECM know the position of the crankshaft as well as the engine's RPM.

Location:

Usually found on the cam cover, either at the front or back of the camshafts

Function:

Reads the position and speed of the camshafts

Description:

The camshaft position sensor looks and functions much like the crankshaft position sensor. It allows the ECM to know the speed and positions of the camshafts, which provide more information on top of the CKP sensor information. The camshafts control the intake and exhaust values, and this sensor lets the ECM know what values are currently opened. As mentioned above, the ECM uses the combined input from CKP and CMP sensors to verify that timing between the crankshaft and camshafts is accurate.

The CMP sensor is a Hall-effect sensor, meaning it monitors magnetic fields. This sensor is always located close to a ring gear with teeth, which located on the camshaft. As the gear spins, the head of the sensor faces the teeth and reads the pattern as they rotate. The CMP sensor pulses volts of electricity with each tooth that passes.

The key to this system is that the gear or wheel has one tooth missing around the edge. As this passes the CMP sensor, it skips an electrical pulse, and this is what lets the ECM know the position and speed the camshaft is travelling.

Most modern cars have DOHC engines (double overhead camshafts), meaning that for each bank, or row, of cylinders, there are two camshafts. Inline engines typically have two camshafts and therefore two CMP sensors. For V engines, two banks = 4 camshafts and 4 CMP sensors.

Location:

Side of throttle body

Function:

Monitors how far open the throttle value is

Description:

The throttle position sensor allows the ECM to know how much air is entering the intake manifold based on how open the throttle valve is. When you press the accelerator pedal, it sends an elecrical signal to the throttle control motor in the throttle body. This turns the throttle shaft, which the throttle plate is attached to. Knowing the position of the throttle plate paired with the information from the mass air flow sensor, the ECM determines how to adjust fuel injection and ignition timing based on the amount of air coming in. A further-open throttle valve means more airflow, resulting in a need for more fuel as the car accelerates.

In older cars, the TPS sensor was directly connected to the throttle shaft and rotated with it. More modern cars now use various other kinds of non-contact sensors for their TPS, including Hall-effect and inductive sensors.

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Location:

Inside air intake pipe, between air filter and throttle body

Function:

Measures volume and density of incoming air

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