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 (MAF) sensor and the fuel tank pressure (FTP) 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.

### Conditions for Setting the DTC

The APP sensor 2 voltage is more than 4.8 volts or less than 0.2 volts.

or

The voltage of APP sensor 1 is 0.2 volts more than expected in part throttle range or 1 volt more than expected in full throttle range.

### 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. If the DTC resets, check all of the circuits to the APP sensors for high resistance. Resistance as low a 2 ohms in the APP sensor circuits can affect the operation of the sensors.

With the ignition ON and the engine OFF, view the APP sensor 1 and the APP sensor 2 with a scan tool. Slowly depress the accelerator pedal. If one sensor value changes and the other sensor value does not change, test the sensor circuits for high resistance or shorts. Refer to Circuit Testing in Wiring Systems. If the circuits are OK, replace the APP sensor.

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.

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

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. The APP sensor 2 and the throttle position sensors all share the same 5-volt source in the ECM. A short to ground or to voltage on the 5-volt reference circuit for the TP sensor will affect the operation of APP sensor 2.

2. The ECM performs a comparison of the signals from both APP sensors during the entire range of operation. If the DTC does not set with the key ON and the accelerator pedal released, actuating the throttle may cause the DTC to set.

3. This step is to test the integrity of the APP sensor 2 signal circuit. The APP sensor 2 data parameter on the scan tool should read near 5 volts when connected to the 5-volt reference circuit.

4. The 5-volt reference for the TP sensors and APP sensor 2 are connected inside the ECM. A short to voltage on the TP sensor 5-volt reference circuit will affect the operation of APP sensor 2.

#### DTC P1280 Accelerator Pedal Position (APP) Sensor 2 Circuit

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. Are DTCs P1120 or P1220 also set? | -- | Got to Diagnostic Trouble Code (DTC) List | Go to Step 3
3 |

1. Turn ON the ignition, with the engine OFF.
2. Using a scan tool, observe the APP sensor 2 parameter in the engine control module data list.

Does the scan tool indicate that the APP sensor 2 parameter is within the specified amount?

0.2- 0.5 V

Go to Step 4

Go to Step 6

4 |

1. Turn OFF the ignition for 30 seconds.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, clear the DTC information.
4. Move the APP harness and related connectors while monitoring the DTC information.

Does the harness movement cause this DTC to reset?

--

Go to Step 18

Go to Step 5

5 |

1. Continue to monitor the DTC information with the scan tool.
2. Slowly depress the accelerator pedal to wide open throttle and then slowly return it to the closed position. Repeat this action several times.

Does this DTC reset?

--

Go to Step 6

Go to Diagnostic Aids

6 |

1. Turn OFF the ignition.
2. Disconnect the APP sensor.
3. Turn ON the ignition, with the engine OFF.
4. Using a scan tool, observe the APP sensor 2 parameter.

Does the scan tool indicate that the APP sensor 2 parameter is less than the specified value?

0.2 V

Go to Step 7

Go to Step 16

7 | Measure the voltage between the 5-volt reference circuit of the APP sensor 2 and battery ground using a DMM. Is the voltage within the specified range? | 4.8-5.2 V | Go to Step 8 | Go to Step 12
8 |

1. Turn OFF the ignition.
2. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the APP sensor 2 and the signal circuit of the APP sensor 2.
3. Turn ON the ignition, with the engine OFF.
4. Using a scan tool, observe the APP sensor 2 parameter.

Does the scan tool indicate that the APP sensor 2 parameter is more than the specified value?

4.8 V

Go to Step 9

Go to Step 15

9 |

Important: Make sure the ECM has shut down prior to measuring the reference ground circuit resistance. This can be verified by the loss of communication on the scan tool.

1. Turn OFF the ignition for 30 seconds.

Important: Do not use a test lamp in order to test the continuity of the reference ground. Damage to the ECM will result.

2. Measure the resistance from the reference ground circuit of the APP sensor 2 to battery ground.

Is the resistance less than the specified value?

5 ohms

Go to Step 20

Go to Step 10

10 |

1. Disconnect the ECM connector.
2. Test the reference ground circuit of APP sensor 2 for an open or for high resistance.
3. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 11

11 | Measure the resistance from the ground stud at the ECM bracket to battery ground. Is the resistance less than the specified value? | 5 ohms | Go to Step 21 | Go to Step 19
12 | Is the voltage less than the specified value? | 5 V | Go to Step 14 | Go to Step 13
13 | Test the 5-volt reference circuit of the APP sensor 2 for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 17
14 | Test the 5-volt reference circuit of the APP sensor 2 for a short to ground, high resistance, or an open. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 21
15 | Test the signal circuit of the APP sensor 2 for a short to ground, for high resistance, or for an open. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 21
16 | Test the signal circuit of the APP sensor 2 for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 23
17 |

1. Test for a short to voltage on the 5-volt reference circuit of TP sensor.
2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 23

18 | Repair the harness or connections as necessary. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 24 | --
19 | Repair the open or high resistance in the ECM ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 24 | --
20 | Test for a poor connection or terminal tension at the harness connector of the APP sensor 2. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 22
21 | Test for a poor connection or terminal tension at the harness connector of the engine control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 24 | Go to Step 23
22 | Replace the APP sensor. Refer to Accelerator Pedal Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 24 | --
23 | Important:

• | Perform the idle learn procedure when replacing the ECM or the throttle body.

• | This vehicle is equipped with a theft deterrent system which interfaces with the engine control module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle.

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the action?

--

Go to Step 24

--

24 |

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 25

Go to Step 2

25 | 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