Accelerator Pedal Position Sensor: Description and Operation

Electronic Power Control (EPC)
Function of EPC systems
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 is transmitted to the engine control module by two sensors (variable resistors; mounted in one housing) which are connected to the accelerator pedal.
The position of the accelerator (drivers requirement) is the main input value for the engine control module.

An electric motor (throttle actuator) in the throttle valve control module -J338- actuates the throttle valve over the entire range of engine speeds and load.

The throttle valve is operated by the throttle actuator under instructions from 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 sender. This means that when the accelerator 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 sender.
This means that the throttle valve can already be completely open even though the accelerator pedal is depressed half way. This has the advantage of preventing throttle losses at the throttle valve.

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

It is wrong to believe that electronic throttle control only consists of two components. It is a system which contains all components needed to help determine, regulate, and supervise the throttle valve position (e.g. the throttle position sensor which measures the accelerator position the throttle valve control module, the EPC indicator lamp, the engine control module).