Accelerator Pedal Position Sensor: Description and Operation

Function of EPC system
With the EPC system the throttle valve is not operated by the throttle pedal via a cable. There is no mechanical connection between accelerator and throttle valve.

The position of the accelerator pedal is transmitted to the engine control module by two accelerator pedal position sensors (variable resistors; mounted in one housing) which are connected to the accelerator pedal.

The position of the accelerator pedal (drivers requirement) is the main input value for the engine control module.

The throttle valve is operated over the complete revolution and load range by an electric motor (throttle valve positioner) in the throttle valve control module.

The throttle valve is operated by the throttle valve positioner which is controlled by the engine control module.

When the engine is not running and the ignition is switched on the engine control module moves the throttle valve exactly as prescribed by the accelerator pedal position sensor. This means that when the accelerator pedal is depressed halfway the throttle valve positioner opens the throttle valve by the same amount. The throttle is then approximately half open.

When the engine is running (under load) the engine control module can open or close the throttle valve independently of the accelerator pedal position sensor.

This means that the throttle valve can already be completely open even though the accelerator pedal is depressed halfway. This gives vastly improved consumption and exhaust emission levels at certain load conditions.

After evaluating the torque requirements of various components (e.g. air conditioning, automatic transmission, ABS/ESP etc.), the engine control module calculates the optimal throttle valve opening angle for the respective situation.

This also gives vastly improved consumption and exhaust emission levels at certain load conditions.

EPC is a system comprising all components which contribute to determining, controlling or monitoring the position of the throttle valve, e.g. accelerator pedal position sensor, the throttle valve control module, the EPC warning lamp, the engine control module and so on.

Observe safety precautions
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