For 1990-2009 cars

### Circuit Description

The accelerator pedal position (APP) sensor is made up of 2 sensors that are housed inside one assembly. The APP sensor is located on a bracket above the accelerator pedal. The engine control module (ECM) supplies a separate 5-volt reference and the ground circuit for each of the sensors. The 5-volt reference for APP sensor 1 is supplied from the same source in the ECM as the 5-volt reference for the mass air flow sensor and the fuel tank pressure sensor. The 5-volt reference for APP sensor 2 is supplied from the same source in the ECM as the 5-volt reference for the throttle position sensors. The 5-volt reference voltage for all of the sensors is supplied on separate ECM terminals, but the terminals are connected internally to the shared voltage supply. The APP sensor sends a signal from each of the sensors to the ECM indicating the acceleration demand of the driver. The ECM actuates the throttle plates based on this information.

The APP sensor 1 signal voltage increases as the throttle opens, from about 0.4 volt at closed throttle to above 3.5 volts at wide open throttle (WOT). The APP sensor 2 signal voltage also increases as the throttle opens, but at a slightly different rate. The APP sensor 2 signal voltage increases from about 0.2 volt at closed throttle to about 1.8 volts at wide open throttle. The APP sensor 1 is the main control of the system. The APP sensor 2 is used for comparison of the APP sensor 1. The ECM constantly monitors these two sensors and if the sensors are not within a calibrated value, a diagnostic trouble code (DTC) will set.

### Conditions for Running the DTC

• | The battery voltage is more than 7 volts.

• | The accelerator pedal is leaving the idle position.

### Conditions for Setting the DTC

The voltage difference between APP sensor 1 and APP sensor 2 is not correct when leaving idle.

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

### Conditions for Clearing the MIL/DTC

• | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• | 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 emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Diagnostic Aids

The ECM compares the signal of each of the accelerator pedal position sensor to each other throughout the entire range of operation. Clear the DTCs and actuate the throttle through the entire range with the ignition ON and the engine OFF.

Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

Inspect the APP sensor mounting bolts and the actuator arm. The bolts should be tight. If the APP sensor is loose, a false reading could be sent to the ECM.

Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems for intermittent conditions.

### Test Description

The number below refers to the step number on the diagnostic table.

1. Any circuit faults on either APP sensor 1 or sensor 2 will set one of the DTCs listed. Refer to the appropriate table for diagnosis.

#### DTC P1271 Accelerator Pedal Position (APP) Sensor 1 - 2 Correlation

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Using a scan tool, observe the DTC information. Is DTC P0100, P1120, P1220, P1275, or P1280 also set? | -- | Go to Diagnostic Trouble Code (DTC) List | Go to Step 3
3 |

1. Turn OFF the ignition.
2. Disconnect the APP sensor electrical connector.
3. Disconnect the ECM.
4. Use a DMM to measure the resistance of the following circuits for each of the APP sensors:

• | The reference ground circuit

• | The signal circuit

• | The 5-volt reference circuit

Did any of the circuits measure more than the specified value?

5 Ohms

Go to Step 5

Go to Step 4

4 |

1. Test for a short between any of the circuits in the APP sensor harness.
2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 7

Go to Step 6

5 | Repair the high resistance in the circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 7 | --
6 | Replace the APP sensor. Refer to Accelerator Pedal Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 7 | --
7 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 8

Go to Step 2

8 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK