Electronic Throttle Control Module: Description and Operation

Electronic Power Control

With an Electronic Power Control (EPC) system, the throttle valve is not operated by a cable from the accelerator pedal. There is no mechanical connection between the accelerator pedal and the throttle valve. The throttle valve is controlled electronically.

There are 3 main components to the system:

• Accelerator pedal

• Throttle valve control module

• Engine Control Module (ECM)

The accelerator pedal module consists of 2 redundant pedal position sensors (accelerator pedal position sensor 1 and accelerator pedal position sensor 2 ) located on the pedal assembly. The accelerator pedal position is one of the primary inputs to the ECM.

The throttle valve control module contains the following:

• EPC throttle drive

• EPC throttle drive angle sensor 1

• EPC throttle drive angle sensor 2

The throttle angle sensors are also a primary input to the ECM for EPC.

The ECM takes inputs from the throttle and pedal sensors along with various engine sensors to determine engine speed, load and transmission shifts. Operation of the throttle valve occurs via an electric motor.

The throttle valve is operated according to commands from the ECM to the throttle valve control module.

With the engine off and the ignition turned on, the throttle valve moves according to primary input from the accelerator pedal position sensor. The engine load, speed or other sensor inputs are not a contributing factor with the engine off. If the accelerator pedal is pressed half way, the throttle drive opens the throttle valve to the same degree, for example, the throttle valve is then opened approximately half way.

With the engine running under load (such as towing a trailer or pulling away from a stop), the ECM can operate the throttle valve to a higher percentage of opening than the pedal position percentage based on other sensors or contributing factors (engine load, engine speed and current gear).

For example, under certain conditions the throttle valve could be opened above half throttle even through the accelerator pedal has only been pressed half way. This has the advantage of increasing torque under load. Another example, would be that the throttle valve is reduced to a low engine load condition during a gear change, then returns to match accelerator pedal input for control of throttle valve position upon completion of the gear change. speed control is also maintained by ECM input to the throttle valve control module based on vehicle speed, current gear and load.

If one of the redundant primary sensors of the EPC system fall out of range, a reduced engine power mode will automatically take over with limited throttle control and allow the vehicle to be safely driven to it's destination. If both redundant sensors fail, the throttle control system will default to an approximate 15% opening and no throttle control will be available. This will allow the operator a limp in mode to get the vehicle to a service facility without being stranded.

Whenever a system fault is detected, the electronic power control malfunction indicator lamp in the instrument cluster will illuminate to alert the operator of a system fault.