P0121

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 ignition voltage is greater than 6.4 volts.
^ The engine speed is greater than 300 RPM.
^ There are no in range faults for APP 2 or APP 3 (The PCM checks for high and low voltage faults).

Conditions for Setting the DTC
^ The difference between APP 1 and APP 2 is greater than 0.23 volts (The PCM compares a pre-scaled voltage (internal to the PCM).
^ The difference between APP 1 and APP 3 is greater than 0.50 volts (PCM compares pre-scaled voltage (internal to PCM).
^ The 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 stores in the Failure Records.

Conditions for Clearing the MIL/DTC
^ A History DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use of a Scan tool will clear the DTC codes.

Diagnostic Aids
There are no driveability issues associated with the APP module unless a DTC is present. The most likely cause to this DTC are poor connections or the sensor itself. The least likely is a PCM problem.

An intermittent may be caused by the following:
^ Poor connections
^ Rubbed through wire insulation
^ Broken wire inside the insulation

A scan tool reads APP 1 position in volts. It should read about 0.45 to 0.95 volts 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% pedal travel is acceptable for correct APP operation. Scan the APP 1 sensor while depressing the accelerator pedal with the engine stopped and the ignition ON. Display should vary from about 0.74 volts when the throttle was closed to over about 3.7 volts when the throttle is held at Wide Open Throttle (WOT) position. The following chart will check voltages on all APP circuits to see if they fall in normal ranges. The PCM compares pre-scaled voltages (these are voltages that the scan tool cannot read). The scan tool reads only output voltages.

Test Description
The number(s) below refer to the step number(s) on the Diagnostic Table.
4. This step determines if there is a good 5 volt reference.
5. This step will check for an open in the ground circuit.