GM/Detroit 6.5L ENGINE CONTROLS – DTC P0123 App Sensor Circuit High Voltage

Circuit Description
The accelerator pedal position (APP) module provides a voltage signal that changes relative to accelerator pedal position. There are three sensors located within the APP module that are scaled differently.

Conditions for Running the DTC
• The PCM performs this DTC diagnostic continuously.
• The ignition switch in the ON position.

Conditions for Setting the DTC
• The voltage on the APP 1 sensor is more than 4.75 volts.
• All of the diagnostic set conditions met for 2 seconds.

Action Taken When the DTC Sets
• The service throttle soon lamp will not illuminate when one APP DTC sets. The PCM will only illuminate the service throttle soon lamp when multiple APP DTCs set.
• The PCM records the operating conditions at the time the diagnostic fails. This information will store in the Failure Records.

Conditions for Clearing the MIL/DTC
• A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
• The use of a scan tool.

Diagnostic Aids
There are no driveability issues associated with the APP module unless a DTC is present. The most likely causes of this DTC are poor connections or the sensor itself. The least likely is a PCM problem.
An intermittent may be caused by the following: A scan tool reads APP 1 position in volts. It should read about 0.45 to 0.95 volt with the throttle closed and the ignition ON or at idle. Voltage should increase at a steady rate as the throttle is moved toward wide open throttle (WOT). Also, 90 percent pedal travel is acceptable for correct 0 APP operation. Scan APP 1 sensor while depressing the accelerator pedal with the engine and the ignition ON. Display should vary from about 0.74 volt when the throttle is closed to about 3.7 volts when the throttle is held at wide open throttle (WOT). A P0123 will result if the ground circuit is open or the signal circuit is shorted to voltage.

An intermittent may be caused by any of the following conditions:
• A poor connection
• Rubbed through wire insulation
• A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to intermittents and Poor Connections Diagnosis in Wiring Systems. If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
2. This step determines if DTC P0123 is the result of a hard failure or an intermittent condition.


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