P2138

Schematic:

The accelerator pedal assembly contains two accelerator pedal position (APP) sensors with two independent 5 volt supplies, two independent grounds, and two 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 0.98 to 4.16 volts (+/-0.1), while the voltage on APP sensor 2 signal increases from 0.49 to 2.08 volts (+/-0.1). 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.

DTC PARAMETERS
DTC P2138 will set if APP sensor 2 are does not change by more than 40 mV from when APP sensor 1 transitioned from under 1.27 volts to over 1.27 volts when:
^ Stored APP sensor 1 reading below 1.27 volts was present for longer than 100 ms and the stored APP sensor 1 reading above 1.27 volts was present for longer than 100 ms
^ Main relay voltage is greater than 7.0 volts
^ Ignition is On

DTC P2138 diagnostic runs continuously once the above conditions have been met.

P2138 is a type A and C DTC.

NOTE: The MIL will only illuminate if the fault is present for longer than 5 seconds.

DIAGNOSTIC AIDS

IMPORTANT: If an APP low or high voltage circuit fault DTC is set, diagnose that DTC first. An intermittent circuit fault may also set this DTC.

To locate an intermittent problem, use Scan tool to monitor APP SENSOR 1 and APP SENSOR 2 with ignition On, engine Off. Press accelerator pedal very slowly from the rest to full position, while monitoring each sensor voltage range. Watch for a sharp change in each of the voltage ranges, which would indicate a problem.

Make sure each APP sensor harness connector terminal is not spread and the connector is free of corrosion or foreign material.

APP sensor 2 should always be one half the voltage value of APP sensor 1 (+/-0.1 volts) during the entire pedal travel range.

REST POSITION FULL TRAVEL

APP SENSOR 1 0.98 4.16
APP SENSOR 2 0.49 2.08

Replace the accelerator pedal assembly if a problem was found.