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 Powertrain Control Module (PCM) performs this Diagnostic Trouble Code (DTC) diagnostic continuously.
^ The ignition voltage is more than 6.4 volts.
^ The engine speed is more than 300 RPM.
^ There are no in range faults for the APP 2 sensor or the APP 3 sensor (PCM checks for high and low voltage faults).

CONDITIONS FOR SETTING THE DTC
^ The difference between the APP 1 sensor and the APP 2 sensor is more than 0.23 volts (PCM compares pre-scaled voltage, internal to PCM).
^ The difference between the APP 1 sensor and the APP 3 sensor is more than 0.50 volts (PCM compares pre-scaled voltage, internal to PCM).
^ All of the diagnostic set 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.
^ Use a scan tool in order to clear the DTC.

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. 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 the APP 1 position in volts. It should read about 0.45-0.95 volt 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 off and the ignition ON. Display should vary from about 0.74 volt when the throttle is closed to over about 3.7 volts when the throttle is held at Wide Open Throttle (WOT). 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.

An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Electrical Intermittents in Diagrams.

If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Diagrams.

TEST DESCRIPTION

Steps 1-12:

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.