Function of the Electronic Power Control (EPC) system

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2002 Volkswagen Jetta, 2002 Volkswagen GTI, 2001 Volkswagen Jetta, 2001 Volkswagen GTI, and 2000 Volkswagen Jetta. However, it is still accessible from the selected car via links, so may be relevant.

In the Electronic Power Control (EPC) system, the throttle valve is not actuated by a cable from the accelerator. There is no mechanical connection between the accelerator and throttle valve.

The accelerator position is communicated to the engine control module by two throttle position sensors (variable resistance, accommodated in a casing), which are connected to the accelerator.

The accelerator position (determined by the driver) is a main input variable 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 actuated by the throttle actuator under instructions from the engine control module.

When the engine is off and the ignition is turned on, the engine control module controls the throttle actuator precisely, following specifications from the throttle position sensor. That is, if the accelerator is half-way to the floor, then the throttle actuator opens the throttle valve to the same angle; the throttle valve is then opened approximately half-way.

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

As an example, the throttle valve can already be completely open, even though the accelerator has only been pressed half-way down so far. This has the advantage of preventing throttling loss at the throttle valve.

Under certain load conditions, this also results in significantly reduced emissions and improved fuel consumption.

It is wrong to believe that EPC 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 Electronic Power Control (EPC) warning lamp, the engine control module).