P3902 BMW Fault Code

Description:

The Camshaft Position sensor will signal the Engine Control Module when the #1 cylinder is ready for the spark plug to fire (top-dead-center on compression stroke).

The ECM uses the information from this sensor to help calculate fuel delivery and spark timing.

P3902 Code Symptoms :

The original multi-displacement system turned off opposite pairs of cylinders, allowing the engine to have three different configurations and displacements. P3902 code had an elaborate diagnostics procedure, including showing engine trouble codes on the air conditionning display. However, the system was troublesome, misunderstood by customers, and a rash of unpredictable failures led to the technology being quickly retired.

Diagnosis And Repairing P3902

P3902 OBD2 specifically refers to the camshaft (cam) timing. In this case, if the cam timing is over-retarded, the engine light will be illluminated and the code will be set.

How to fix P3902 code ?

• Exhaust gas leaks
• Air fuel ratio (A/F) Sensor 1 Bank 1 circuit poor electrical connection
• Faulty Mass Air Flow (MAF) sensor
• Missing or loose fuel cap

One example of this would be when an bmw automatic car in placed in gear. To prevent the added drag from the torque converter and transmission from reducing the idling speed, the PCM will command the idle control valve to allow more air to enter the engine, while at the same time, adjusting the injector pulse width to inject more fuel to suit the increased amount of air. Note that the idle air control valve is closed by the PCM when the throttle plate is opened to prevent excess air from entering the engine.