P0121

DTC P0121 Accelerator Pedal Position (APP) Sensor 1 Circuit Performance






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 C DTC.

Conditions for Setting the DTC

^ Ignition voltage greater than 6.4 volts.
^ Engine speed greater than 300 RPM.
^ The difference between APP 1 and APP 2 is greater than .23 volts (PCM compares pre-scaled voltage (internal to PCM)).
^ The difference between APP 1 and APP 3 is greater than .50 volts (PCM compares pre-scaled voltage (internal to PCM)).
^ No in range faults for APP 2 or APP 3 (PCM checks for high and low voltage faults).
^ Conditions met for 2 seconds.

Action Taken When the DTC Sets

^ The input from APP sensor is ignored.
^ A current and history DTC will set but it will not turn on the "Service Throttle Soon" lamp.
^ 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 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).
^ Use of a Scan Tool

Diagnostic Aids

A scan tool reads APP position in volts. It should read about .45 to .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 .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 can't read). The scan tool reads only output voltages.

Test Description

Number(s) below refer to the number(s) on the diagnostic table. This step determines if there is a good 5 volt reference.

2. This step will check for an open in the ground circuit.