GM Service Manual Online
For 1990-2009 cars only

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 and the throttle actuator control (TAC) module. Each sensor has a unique functionality. The APP sensor 1 signal increases 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 decreases 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 decreases from around 3.8 volts at 0 percent pedal travel to below 3.1 volts at 100 percent pedal travel. Notice that the signal circuits for APP sensor 2 and APP sensor 3 pull up to 5-volts and the APP sensor 1 signal circuit is referenced to low reference within the TAC module.

Conditions for Running the DTC

    • DTCs P0606, P1517, or P1518 are not set.
    • The ignition is in the crank or run position.
    • The ignition voltage is greater than 5.23 volts.

Conditions for Setting the DTC

    • The APP sensor 3 voltage is less than 01.63 volts or greater than 4.28 volts.
    • All 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 P1285 set, a DTC P1286 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 number below refers to the step number on the diagnostic table.

  1. 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.

DTC P1285 - Accelerator Pedal Position (APP) Sensor 3 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

Important: If DTC P1518 or P1220 is also set, refer to Diagnostic Trouble Code (DTC) List for further diagnosis.

  1. Turn ON the ignition, with the engine OFF.
  2. Use a scan tool in order to observe the APP sensor 3 voltage parameter.

Does the scan tool indicate APP sensor 3 voltage within the specified values?

3.29-4.28 V

Go to Step 3

Go to Step 6

3

Fully depress the accelerator pedal to the wide open throttle (WOT) position.

Does the scan tool indicate APP sensor 3 voltage within the specified values?

1.63-3.1 V

Go to Step 4

Go to Step 6

4

  1. Turn OFF the ignition for 15 seconds.
  2. Turn ON the ignition, with the engine OFF.
  3. Use a scan tool in order to observe the diagnostic trouble code (DTC) option.
  4. Lightly touch and move the related engine wiring harnesses and connectors for the APP sensor while monitoring the DTC info status.

Did this DTC fail this ignition during the above test?

--

Go to Step 20

Go to Step 5

5

Slowly depress the accelerator pedal to WOT and then slowly return the accelerator pedal to the released position.

Did this DTC fail this ignition during the above test?

--

Go to Step 21

Go to Diagnostic Aids

6

  1. Disconnect the APP sensor harness connector.
  2. Use a DMM in order to test the APP sensor 3 signal circuit for voltage.

Does the DMM indicate APP sensor 3 signal voltage within the specified values?

3.94-6.06 V

Go to Step 11

Go to Step 7

7

  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the APP sensor circuits.
  3. Turn ON the ignition, with the engine OFF.
  4. Use a DMM in order to test the APP sensor 3 signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 8

8

Use a DMM in order to test the APP sensor 3 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 25

Go to Step 9

9

Use a DMM in order to test the APP sensor 3 signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 10

10

  1. Disconnect the other TAC module harness connector.
  2. Use a DMM in order to test for a short between the APP sensor 3 signal circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

11

Use a DMM in order to test the APP sensor 3, 5-volt reference circuit for voltage.

Does the DMM indicate voltage within the specified values?

3.94-6.06 V

Go to Step 16

Go to Step 12

12

  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the APP sensor circuits.
  3. Turn ON the ignition, with the engine OFF.
  4. Use a DMM in order to test the APP sensor 3, 5-volt reference circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 13

13

Use a DMM in order to test the APP sensor 3, 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 25

Go to Step 14

14

Use a DMM in order to test the APP sensor 3, 5-volt reference circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 15

15

Use a DMM in order to test for a short between the APP sensor 3, 5-volt reference circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

16

With a DMM connected between the APP sensor 3 low reference circuit and the APP sensor 1 low reference circuit, measure the resistance.

Does the DMM indicate resistance within the specified values?

0-5 ohms

Go to Step 18

Go to Step 17

17

  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the APP sensor circuits.
  3. Use a DMM in order to test the APP sensor 3 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 25

Go to Step 23

18

  1. Use a scan tool in order to observe the APP sensor 3 voltage parameter.
  2. Connect a fused jumper between the APP sensor 3 signal circuit and the APP sensor 3 low reference circuit at the APP sensor harness connector.

Does the scan tool indicate APP sensor 3 voltage at the specified value?

0 V

Go to Step 19

Go to Step 24

19

  1. Turn OFF the ignition.
  2. Disconnect the TAC module.
  3. Use a DMM in order to test for a short between the APP sensor 3 signal circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 21

20

Repair the intermittent connection as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 25

--

21

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 25

Go to Step 22

22

Replace the APP sensor assembly. Refer to Accelerator Pedal Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 25

--

23

Inspect for poor connections at the harness connector 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 25

Go to Step 24

24

Replace the TAC module. Refer to Electronic Throttle Actuator Control Module Replacement .

Did you complete the replacement?

--

Go to Step 25

--

25

  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 26

Go to Step 2

26

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