P0121

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

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-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 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 a scan tool in order to clear the DTCs

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 problem.

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

A scan tool reads the APP 1 position in volts. It should read approximately 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. 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 Wide Open Throttle (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
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.