Fuel Delivery and Air Induction: Description and Operation

Function of electronic throttle system

With the electronic throttle (drive by wire) the throttle valve is not operated by a cable connected to the accelerator pedal. There is no mechanical link between the accelerator and the throttle valve.

The position of the accelerator pedal is communicated to the Engine Control Module (ECM) by two accelerator position sensors (variable resistors, both installed in a single housing) which are connected to the accelerator pedal.

The accelerator pedal position (as determined by the driver) is one of the main input values for the engine control module.

The throttle valve is actuated by a servomotor (throttle valve positioner) in the throttle valve control module over the full range of engine speeds and load conditions.

The throttle valve positioner actuates the throttle valve according to the commands it receives from the engine control module.

When the engine is running (i.e. under load) the engine control module can open and close the throttle valve freely, independently of the signals being sent by the accelerator position sender.

The electronic throttle is not simply a combination of two or three components, but rather a complete system comprising all the elements that together determine the position of the throttle valve and also control and monitor it. For example, the accelerator position sensor, throttle valve control module, EPC malfunction indicator light, engine control module etc.