DTC P2138: App Sensor Correlation: Description

WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The accelerator pedal assembly contains two Accelerator Pedal Position (APP) sensors with two independent 5-volt supplies, 2 independent grounds, and 2 independent signal circuits that vary resistance according to changes in accelerator pedal position. The ECM measures the signal voltage from each APP sensor, which are reduced values of the ECM 5-volt references. As the accelerator pedal moves from the rest to full position, the voltage on APP sensor 1 signal increases from 0.88-1.08 to 4.06-4.20 volts, while the voltage on APP sensor 2 signal increases from 0.39-0.59 to 1.98-2.18 volts. The ECM monitors each APP signal circuit for faults as well as performing a comparison check between the sensor 1 and 2 signals. DTC P2138 will set if APP sensor 2 signal voltage does not change by more than a calibrated amount after APP sensor 1 signal transitioned from under to over a calibrated set point or if the signals no longer correlate with each other.