DTC P1278 Accelerator Pedal Position (APP) Sensor 1 Circuit High Voltage. Generic Unit Repair 1999

For 1990-2009 cars only

Makes 🢒 Generic 🢒 1999 🢒 Unit Repair 🢒 DTC 🢒 DTC P1278 Accelerator Pedal Position (APP) Sensor 1 Circuit High Voltage

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 PCM performs this DTC diagnostic continuously.

•	DTC P1635 is not set.

Conditions for Setting the DTC

•	The voltage on the APP 1 sensor is greater than 4.75 volts.

•	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 will store in the Failure Records.

Conditions for Clearing the MIL/DTC

•	A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.

•	Use of a scan tool

Diagnostic Aids

Important: Remove any debris from the PCM module connector surfaces before servicing the PCM module. Inspect the PCM module connector gaskets when diagnosing/replacing the module. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM module.

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:

A scan tool reads APP 1 position in volts. 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 percent pedal travel is acceptable for correct 0 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 about 3.7 volt when throttle is held at Wide Open Throttle (WOT) position. A DTC P1278 will result if the ground circuit is open or the signal circuit is shorted to voltage.