For 1990-2009 cars

### Circuit Description

The accelerator pedal position (APP) sensor is mounted on the accelerator pedal assembly. The sensor is actually 3 individual APP sensors within one housing. Three separate signal, low reference, and 5-volt reference circuits connect the APP sensor assembly to the throttle actuator control (TAC) module. Each sensor has a unique functionality. The APP sensor 1 signal is pulled up to reference voltage as the accelerator pedal is depressed, from below 1.0 volt at 0 percent pedal travel, pedal at rest, to above 2.0 volts at 100 percent pedal travel, pedal fully depressed. The APP sensor 2 signal is pulled down to low reference from above 4.0 volts at 0 percent pedal travel to below 2.9 volts at 100 percent pedal travel. The APP sensor 3 signal is pulled down to low reference from above 3.8 volts at 0 percent pedal travel to below 3.1 volts at 100 percent pedal travel. Throttle position (TP) sensor 1 and APP sensor 1 share a 5-volt reference circuit that are connected within the TAC module. TP sensor 2 and APP sensor 2 share a 5-volt reference circuit that are connected within the TAC module. If only one APP sensor diagnostic trouble code (DTC) is set, the redundant APP systems allow the TAC system to continue operating normally. One APP sensor DTC will not cause the Reduced Engine Power message to be displayed. Two APP sensor DTCs for the same sensor also will not cause the Reduced Engine Power message to be displayed. If an out of range condition is detected with this APP sensor, this DTC will be set.

### Conditions for Running the DTC

• | DTC P0606, P1517, or P1518 are not set.

• | The ignition switch is in the crank or run position.

• | The ignition voltage is greater than 5.23 volts.

### Conditions for Setting the DTC

• | APP sensor 2 disagrees with APP sensor 1 by more than 10.5 percent and APP sensor 2 disagrees with APP sensor 3 by more than 13.0 percent.

• | All of the above conditions are present for less than 1 second.

### 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.

• | If one or more APP sensor DTCs are set for a single APP sensor, the following occurs:

- | The control module will not command Reduced Engine Power mode.

- | The control module will use the remaining two APP sensors to calculate throttle response.

• | If certain multiple APP sensor DTCs are set for more than one APP sensor, the following occurs:

- | The control module commands Reduced Engine Power mode.

- | The APP indicated angle is limited to a predetermined value to limit the amount of throttle control.

- | The message center displays Reduced Engine Power.

• | If all three APP sensors are out of range, the following occurs:

- | The control module commands Reduced Engine Power mode.

- | The APP indicated angle is limited to 0 percent. The control module only allows the engine to idle.

- | The message center displays Reduced Engine Power.

### 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.

• | Clear the DTC with a scan tool.

### Diagnostic Aids

• | Inspect the TAC module connectors for signs of water intrusion. When this occurs, multiple DTCs could be set with no circuit or component conditions found during diagnostic testing.

• | When the TAC module detects throttle movement with a DTC P1280 set, a DTC P1281 also sets.

• | When the TAC module detects a condition within the TAC system, more than one TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture Info.

• | For an intermittent, refer to Intermittent Conditions .

### Test Description

The numbers below refer to the steps numbers in the diagnostic table.

1. This step determines if a communication condition exists.

2. This step isolates an internal APP sensor failure. The condition may only occur at a certain accelerator pedal position. Monitoring the APP angles for sensor 1 and sensor 3 is an accurate way of verifying the actual position of the pedal.

3. The APP sensor 2 shares a common 5-volt reference circuit with the TP sensor 2. Monitoring the TP sensor 2 voltage aids in diagnosing the APP sensor 5-volt reference and low reference circuits. If the scan tool displays near 0 volts then the circuits are OK.

4. When the TAC module detects a condition within the TAC system, more than one TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture Info.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Is DTC P1518 also set? | -- | Go to DTC P1518 | Go to Step 3
3 | Important: Do not depress the accelerator pedal.

1. Start the engine.
2. Use a scan tool in order to observe DTC info.

Did any other TAC module or APP sensor DTCs set except P1125?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 4

4 | Use a scan tool in order to observe the APP sensor Agree/Disagree parameters. Does the scan tool indicate Disagree for any of the APP sensors Agree/Disagree parameters? | -- | Go to Step 6 | Go to Step 5
5 |

1. Turn ON the ignition, with the engine OFF.
2. Use a scan tool in order to observe the APP sensor angles for all 3 APP sensors.
3. Slowly depress the accelerator pedal, stopping at 25, 50, 75, and 100 percent.
4. Slowly release the accelerator pedal, stopping at 75, 50, 25, and 0 percent.

Does the scan tool indicate APP sensor 2 angle within 10.5 percent of the APP sensor 1 angle and APP sensor 2 angle within 13 percent of the APP sensor 3 angle during the above test?

--

Go to Diagnostic Aids

Go to Step 6

6 |

1. Turn OFF the ignition.
2. Disconnect the APP sensor harness connector.
3. Connect a fused jumper between the APP sensor 2 5-volt reference circuit and ground.
4. Turn ON the ignition, with the engine OFF.
5. Use a scan tool in order to observe the TP sensor 2 voltage parameter.

Does the scan tool indicate TP sensor 2 voltage at the specified value?

0 V

Go to Step 7

Go to Step 12

7 |

1. Connect a fused jumper between the APP sensor 2 5-volt reference circuit and the APP sensor 2 low reference circuit.
2. Use a scan tool in order to observe the TP sensor 2 voltage parameter.

Does the scan tool indicate TP sensor 2 voltage at the specified value?

0 V

Go to Step 8

Go to Step 11

8 |

1. Turn OFF the ignition.
2. Disconnect the TAC module harness connector containing the APP circuits.
3. Use a DMM in order to test the APP sensor 2 signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 9

9 |

1. Turn OFF the ignition.
2. Use a DMM in order to test for a short between the APP sensor 2 signal circuit and all other APP circuits at the APP sensor harness connector.

Does the DMM indicate a short to another circuit?

--

Go to Step 10

Go to Step 13

10 |

1. Disconnect the TAC module harness connector containing the APP sensor circuits.
2. Use a DMM in order to test for a short between the APP sensor 2 signal circuit and all other APP circuits at the APP sensor harness connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 13

11 |

1. Turn OFF the ignition.
2. Disconnect the TAC module harness connector containing the APP circuits.
3. Use a DMM in order to test the APP sensor 2 5-volt reference circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 12

12 | Use a DMM in order to test the APP sensor 2 low reference circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14
13 | Inspect for poor connections at the harness connector of the APP sensor. 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 17 | Go to Step 15
14 | Inspect for poor connections at the harness connectors of the TAC 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 17 | Go to Step 16
15 | Replace the accelerator pedal assembly. Refer to Accelerator Pedal Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 17 | --
16 | Replace the TAC module. Refer to Electronic Throttle Actuator Control Module Replacement . Did you complete the replacement? | -- | Go to Step 17 | --
17 |

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 18

Go to Step 2

18 | 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