Electronic Power Control (EPC) System, Significance

Electronic Power Control (EPC) System

Functional description of EPC system
With the EPC system, the throttle valve is not actuated by way of a cable from the accelerator pedal. There is no mechanical link between the accelerator pedal and the throttle valve.

The position of the accelerator pedal is signalled to the engine control module by two accelerator pedal position senders (variable resistors in a joint housing) which are connected to the accelerator pedal.

The accelerator pedal position (driver input) is one of the main input variables for the engine control module.

The throttle valve is operated by means of an electric motor (throttle valve actuator) in the throttle valve control module over the entire engine speed and load range.

The throttle valve is operated by the throttle valve actuator as specified by the engine control module.

With the engine stopped and the ignition switched on, the engine control module regulates the throttle valve actuator precisely in line with the specifications of the accelerator pedal position sender. In other words, when the accelerator pedal is depressed halfway the throttle valve actuator opens the throttle valve to the same extent and the throttle valve is then roughly half open.

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

It is thus possible, for example, for the throttle valve to be fully open although the accelerator pedal has only been depressed halfway. This has the advantage of avoiding throttling losses at the throttle valve.

Under certain load conditions, this system also results in considerable improvements as regards pollutant emissions and fuel consumption.

The required engine torque can be achieved by the engine control module by way of an optimum combination of throttle valve cross-section and charge pressure.

It would, however, be inappropriate to think of the EPC system in terms of one or two components. On the contrary, it includes all the units needed to help determine, control and monitor the position of the throttle valve (e.g. accelerator pedal position sender, throttle valve control module, EPC warning lamp, engine control module...).

Electronic Power Control (EPC) warning lamp -K132- in instrument cluster
"EPC" is the abbreviation for Electronic Power Control, i.e. electronic engine output control (electronic throttle).

After the ignition is switched on, the engine control module checks all components of relevance to operation of EPC system.

The engine control module activates the EPC warning lamp following ignition switch-on. Shortly after the engine is started, the EPC lamp goes out if the engine control module has not recognized any faults in the EPC system and there is also no problem with the actuation of the lamp by the engine control module.

If faults in the EPC system are detected during engine operation, the engine control module activates the EPC lamp (these faults are marked in the fault table). At the same time, an entry is made in the engine control module fault memory.