Accelerator Pedal Position Sensor: Description and Operation

ACCELERATOR PEDAL POSITION (APP) SENSOR

The APP sensor is an input to the powertrain control module (PCM) and is used to determine the amount of torque requested by the operator. Depending on the application either a 2-track or 3-track APP sensor is used.

2-Track APP Sensor

2-Track APP Sensor:

There are 2 pedal position signals in the sensor. Both signals, APP1 and APP2, have a positive slope (increasing angle, increasing voltage), but are offset and increase at different rates. The 2 pedal position signals make sure the PCM receives a correct input even if 1 signal has a concern. The PCM determines if a signal is incorrect by calculating where it should be, inferred from the other signals. If a concern is present with one of the circuits the other input is used. There are 2 reference voltage circuits, 2 signal return circuits, and 2 signal circuits (a total of 6 circuits and pins) between the PCM and the APP sensor assembly. The reference voltage circuits and the signal return circuits are shared with the reference voltage circuit and signal return circuit used by the electronic throttle body (ETB) throttle position sensor. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software then converts these degrees to counts, which is the input to the torque based strategy.

3-Track APP Sensor

Typical 3-Track APP Sensor:

There are 3 pedal position signals in the sensor. Signal 1, APP1, has a negative slope (increasing angle, decreasing voltage) and signals 2 and 3, APP2 and APP3, both have a positive slope (increasing angle, increasing voltage). During normal operation APP1 is used as the indication of pedal position by the strategy. The 3 pedal position signals make sure the PCM receives a correct input even if 1 signal has a concern. The PCM determines if a signal is incorrect by calculating where it should be, inferred from the other signals. If a concern is present with one of the circuits the other inputs are used. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software then converts these degrees to counts, which is the input to the torque based strategy. There are 2 reference voltage circuits, 2 signal return circuits, and 3 signal circuits (a total of 7 circuits and pins) between the PCM and the APP sensor assembly. The reference voltage circuits and the signal return circuits are shared with the reference voltage circuit and signal return circuit used by the electronic throttle body (ETB) throttle position sensor.