Accelerator Pedal Position Sensor: Description and Operation

Accelerator Pedal Position Sensor:

The accelerator pedal position sensors 1 and 2 are located on the accelerator pedal assembly. The L81 engine does not use a traditional throttle cable between the accelerator pedal and throttle body. Instead, these two sensors are used to relay accelerator pedal angle input to the Engine Control Module (ECM). These two sensors are two potentiometers that vary resistance depending on pedal movement. As the accelerator pedal moves from rest to the full travel position, the APP sensor 1 signal voltage increases from 0.40 to 3.82 volts (±0.15 volts), while the APP sensor 2 signal voltage increases from 0.22 to 1.92 volts. APP sensor 2 signal voltage is always one-half the value of APP sensor 1 throughout the entire pedal range.

The ECM continuously monitors each APP sensor circuit for low and high voltage faults as well as performing a comparison check between each signal. If an error in one of the sensor signals were detected, the ECM would default to one of the two limp-home modes (limited pedal range (about 10%) with slow acceleration). The vehicle would still be able to travel at highway speeds, as the ECM would now use the opposite sensor for the driver's pedal input.