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.

Conditions for Setting the DTC

^ The PCM performs this DTC diagnostic continuously.

^ The ignition voltage is greater than 6.4 volts.

^ The engine speed is greater than 300 RPM.

^ The difference between the APP 1 sensor and the APP 2 sensor is greater than 0.23 volts (PCM compares prescaled voltage (internal to PCM)).

^ The difference between the APP 1 sensor and the APP 3 sensor is greater than 0.50 volts (PCM compares prescaled voltage (internal to PCM)).

^ There are no in range faults for the APP 2 sensor or the APP 3 sensor (PCM checks for high and low voltage faults).

^ 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 stores in the Failure Records.

Conditions for Clearing the MIL/DTC

^ A History DTC will clear when forty consecutive warm-up cycles that the diagnostic does not fail (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.

^ 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:

^ 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 volt 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 pre-scaled voltages (these are voltages that the scan tool cannot read). The scan tool reads only output voltages.

Test Description

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.