Accelerator Pedal Position Sensor: Description and Operation
ENGINE CONTROL COMPONENTSAccelerator Pedal Position (APP) Sensor
The APP sensor is an input to the powertrain control module (PCM) and determines 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 - Fiesta
There are 2 separate pedal position sensors in the accelerator pedal. The APP1 sensor signal generates a pulse width modulated (PWM) signal to the PCM. The APP1 sensor uses a VPWR circuit, a ground circuit and a signal circuit. Only the APP1 signal circuit is connected to the PCM. The APP2 sensor signal has a positive slope (increasing angle, increasing voltage) and is a class 2 message from the instrument panel cluster (IPC) to the PCM. The APP2 sensor uses a reference voltage circuit, a signal return circuit, and a signal circuit between the IPC and the APP sensor assembly. The two pedal position signals make sure the PCM receives a correct input even if one of the signals has a concern. The PCM determines if a signal is incorrect by calculating an expected position, inferred from the other signals. If a concern is present with one of the circuits the other input is used. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software converts these degrees to counts, which is the input to the torque based strategy. For additional information, refer to Torque-Based Electronic Throttle Control (ETC).
2 Track APP Sensor - All Others
There are 2 pedal position signals in the sensor. Both signals, APP 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 one of the signals 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 pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software converts these degrees to counts, which is the input to the torque based strategy. For additional information, refer to Torque-Based Electronic Throttle Control (ETC).
3 Track APP Sensor
There are 3 pedal position signals in the sensor. Signal 1, APP, 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, APP 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 one 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 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.
