Updated at: 27-07-2023 - By: Lucas

Depending on the piston position in the cylinders, the electronic control unit (ECU) controls injection opening, spark generation, and timing phases (in variable timing engines). Using the crankshaft speed and/or camshaft position signals, the ECU must be able to determine the location of each piston in the cylinder.

The crankshaft and camshaft positions can be used to identify the mechanical position of the pistons in the cylinders during engine operation. The electronic control unit uses this data to conduct engine synchronization (piston position recognition).

Typical ignition order for a 4-cylinder in-line engine is 1 3 4 2. These engines have two pistons that are 180 degrees out of phase with the other two.

How does the camshaft position sensor work?

How Does A Camshaft Position Sensor Work (2)

As a quick summary of how the camshaft position sensor works, the ECU computer is able to determine the exact position of the camshaft.

Fuel ignition point and injection into the cylinder can be calculated using this information.

For the start of the fuel injection sequence and the selective control of the cylinders, the sensor’s information is critical.

The camshaft sensor is a critical component that determines whether or not the car is operating properly. In order to activate the fuel, he instructs the spark plugs. As a result, if it is defective, the automobile will either fail or not start at all.

Because of this, when pistons 1 and 4 are at BDC and 2 and 3 are at TDC, the camshaft position sensor is working properly.

What are BDC and TDC?

Accordingly, here’s what you need to know:


  • is the position in which the piston is closest to the cylinder head, and the axis of the connecting rod is in continuation of the piston axis
  • is the point where the piston speed is zero
  • is the position of the piston at which corresponds to the minimum volume occupied by the motor fluid in the cylinder


  • is the position where the piston is the furthest from the cylinder head and the axis of the connecting rod is the continuation of the piston axis
  • is the point where the piston speed is zero
  • is the position of the piston at which corresponds to the maximum volume occupied by the motor fluid in the cylinder

During the BDC, pistons 1 and 4 are both at the end of the compression stroke and exhaust stroke, respectively. Only at the end of the compression stroke should the piston be ignited or injected.

Because of the direct mechanical link between the crankshaft and the ignition/injection system in earlier engines with mechanical ignition (petrol) or mechanical injection pump (diesel), this synchronization is achieved automatically.

As in modern engines, where the ECU controls both ignition and injection, the sensor data must be used to synchronize the systems. Two methods exist for synchronizing the piston positions:

  • using only crankshaft position information (engine speed)
  • using both crankshaft position and camshaft position information

As an added benefit, the first method does not call for the insertion of a camshaft position sensor. Pistons in the ECU are synchronized through subsequent tests thanks to algorithms in the ECU. There are two pistons in BDC, which means that each cylinder will be progressively injected with gas.

There are two ways to determine which piston is producing torque (raising the speed): by using the crankshaft position sensor and the crankshaft speed sensor.

This method has the drawback of requiring a longer time for the engine to start up. Engine starting is impossible if the crankshaft position sensor (engine speed) malfunctions. Motors with variable timing cannot use this strategy since it necessitates knowledge of the position of the camshaft.

To determine the camshaft position, a position sensor is needed. This is the more usual way. The Hall effect is the most common principle used in sensor design. A metal wheel (pin) attached to the camshaft serves as a guide for determining the correct position of the valve train.

The camshaft position can be read in a variety of ways depending on the type of engine. Pins or wheels with different numbers and sizes of teeth can be utilized.

In a four-cylinder inline engine, the injection computer can tell which piston is on the intake and which is on the exhaust stroke using the signals from the two sensors (crankshaft position and camshaft position).

When the pistons are in their back-to-center position, the crankshaft position sensor detects it (eg 1 and 4). To find out which piston is on the compression stroke, use the camshaft position signal (positive or null).

A metal wheel with many teeth, with variable length, is faster to sync, and in the event of motor position sensor failure, the degraded motor operation is guaranteed by the camshaft position sensor.

Where is the camshaft position sensor located?

How Does A Camshaft Position Sensor Work (3)

There are several different options for where to put the camshaft position sensor on the engine’s cylinder head cover. The camshaft position change system is where the gearwheels are located in variable timing engines. If you can locate the camshaft, you’ll have a lock on it.

The Hall effect sensor for the camshaft position has three pins:

The camshaft position sensor’s OBD 2 error codes are P03xx.

Symptoms of a bad camshaft position sensor

  • starting problems;
  • check engine error icon appears on board;
  • interruptions in connection with the on-board computer;
  • In happy cases, the engine does not pass over 2000 RPM;
  • engine misfires

Is it okay to drive if you have a bad camshaft sensor?

If your vehicle exhibits any of the signs listed above, you should STOP driving it immediately to avoid damaging more components, including expensive ones like the catalytic converter.

Camshaft sensor cleaning

As soon as the car begins to exhibit any of these signs, it is almost always due to a dirty camshaft sensor.

  • Disconnects the minus wire from the car battery.
  • After you do this you need to locate the sensor, as I told you above. It is not in the same place on all cars, so it would be best to use the manual of the car and you will find it much faster.
  • The sensor has 3 cables, note on paper each one where it comes in the initial position to mount them after the correct place.
  • Use a screwdriver and remove the sensor, put it on a clean cloth.
  • Clean it now with a contact spray, then wipe it with another clean cloth.
  • Put it back, connect the 3 cables in the initial position, reconnect the car battery and it’s done.