P0121

Diagnostic Chart:

Wiring Diagram:

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. This is a type D DTC.

Conditions for Setting the DTC

^ The ignition voltage is greater than 6.4 volts.
^ The engine speed is greater than 300 RPM.
^ The difference between APP 1 and APP 2 is greater than 0.23 volts (The PCM compares a prescaled voltage (internal to the PCM)).
^ The difference between APP 1 and APP 3 is greater than 0.50 volts (PCM compares prescaled voltage (internal to PCM)).
^ There are no in range faults for APP 2 or APP 3 (The PCM checks for high and low voltage faults).
^ The conditions met for 2 seconds.

Action Taken When the DTC Sets

^ The input from APP 1 sensor is ignored.
^ This DTC will not turn on the Service Throttle Soon lamp by itself.
^ The throttle will operate normally as long as there is only one malfunction present. If there are two APP malfunctions present, the PCM will turn ON the Service Throttle Soon lamp and limit power. If a third APP malfunction is present, the Service Throttle Soon lamp will be ON and only allow the engine to operate at idle.

Conditions for Clearing the MIL/DTC

^ A History DTC will clear after forty consecutive warm-up cycles during which the diagnostic does not fail (the coolant temperature has risen 5°C (40°F) from start up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle).
^ 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 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:

^ 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 throttle closed and ignition ON or at idle. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT). Also, 90% pedal travel is acceptable for correct APP operation. Scan APP 1 sensor while depressing accelerator pedal with engine stopped and ignition ON. Display should vary from about 0.74 volt when throttle was closed to over about 3.7 volts when 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 prescaled 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.