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 more than 6.4 volts.
^ The engine speed is more 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 more than 0.23 volts - The PCM compares a pre-scaled voltage that is internal to the PCM.
^ The difference between APP 1 and APP 3 is more than 0.50 volts - The PCM compares pre-scaled voltage that is internal to the PCM.
^ The conditions are met for 2 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module stores the DTC information into memory when the diagnostic runs and fails.
^ The malfunction indicator lamp (MIL) will not illuminate.
^ The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
^ The driver information center, if equipped, may display a message.

CONDITIONS FOR CLEARING THE DTC
^ A current DTC Last Test Failed clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
^ Clear the DTC with a scan tool.

DIAGNOSTIC AIDS
There are no driveability issues associated with the APP module unless a DTC is present. The most likely cause of this DTC are faulty connections or the sensor itself. The least likely is a PCM condition.

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

A scan tool reads the APP 1 position in volts. The APP 1 position should read approximately 0.45-0.95 volts with the throttle closed and the ignition ON or at idle. The 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 APP operation. Scan the APP 1 sensor while depressing the accelerator pedal with the engine stopped and the ignition ON. The display should vary from approximately 0.74 volts when the throttle was closed to more than 3.7 volts when the throttle is held at WOT position. The following chart will check the voltages on all the APP circuits to see if the voltages are in normal ranges. The PCM compares pre-scaled voltages, which are voltages that the scan tool cannot read. The scan tool reads only output voltages.

TEST DESCRIPTION

Steps 1-2:

Steps 3-12:

The numbers below refer to the step numbers 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.