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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 85 (Engine Controls - Self-Diagnostics - 8.1L) >> Diagnostic Tests >> DTC P1285: Accelerator Pedal Position Circuit - Sensor 3 >> Diagnostic Procedures

Diagnostic Procedures

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  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: If DTCs P1220 or P1518 is also set, see DTC P1220: THROTTLE POSITION SENSOR 2 - VOLTAGE OUT OF RANGE  or DTC P1518: TAC MODULE SERIAL DATA FAULT  . Diagnose the applicable DTC first.
  2. Turn ON the ignition, with the engine OFF. With a scan tool, observe the APP sensor 3 voltage parameter. Does the scan tool indicate APP sensor 3 voltage is 3.29-4.28 V? If yes, go to next step. If no, 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 is 1.63-3.1 V? If yes, go to next step. If no, go to step  6.
  4. Turn OFF the ignition for 15 seconds. Turn ON the ignition, with the engine OFF. With a scan tool, observe the Diagnostic Trouble Code (DTC) option. Lightly touch and move the related engine wiring harnesses and connectors for the APP sensor while monitoring the DTC info status. Does this DTC fail this ignition cycle during the above test? If yes, go to step  20. If no, go to next step.
  5. Slowly depress the accelerator pedal to WOT and then slowly return the pedal to the released position. Did this DTC fail this ignition cycle during the above test? If yes, go to step  21. If no, see DIAGNOSTIC AIDS .
  6. Disconnect the APP sensor harness connector. With a Digital Multimeter (DMM), test the APP sensor 3 signal circuit for voltage. Does the DMM indicate APP sensor 3 signal voltage is 3.94-6.06 V? If yes, go to step  11. If no, go to next step.
  7. Turn OFF the ignition. Disconnect the TAC module harness connector containing the APP sensor circuits. Turn ON the ignition, with the engine OFF. With a DMM, test the APP sensor 3 signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  8. With a DMM, test the APP sensor 3 signal circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  9. With a DMM, test the APP sensor 3 signal circuit for a short to ground. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  10. Disconnect the other TAC module harness connector. With a DMM, test for a short between the APP sensor 3 signal circuit and all other TAC module circuits. Did you find and correct the condition? If yes, go to step  25. If no, go to step  23.
  11. With a DMM, test the APP sensor 3, 5-volt reference circuit for voltage. Does the DMM indicate voltage is 3.94-6.06 V? If yes, go to step  16. If no, go to next step.
  12. Turn OFF the ignition. Disconnect the TAC module harness connector containing the APP sensor circuits. Turn ON the ignition, with the engine OFF. With a DMM, test the APP sensor 3, 5-volt reference circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  13. With a DMM, test the APP sensor 3, 5-volt reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  14. With a DMM, test the APP sensor 3, 5-volt reference circuit for a short to ground. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  15. With a DMM, test for a short between the APP sensor 3, 5-volt reference circuit and all other TAC module circuits. Did you find and correct the condition? If yes, go to step  25. If no, 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 resistance. Does the DMM indicate resistance is 0-5 ohms? If yes, go to step  18. If no, go to next step.
  17. Turn OFF the ignition. Disconnect the TAC module harness connector containing the APP sensor circuits. With a DMM, test the APP sensor 3 low reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step  25. If no, go to step  23.
  18. With a scan tool, observe the APP sensor 3 voltage parameter. 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 0 V? If yes, go to next step. If no, go to step  24.
  19. Turn OFF the ignition. Disconnect the TAC module. With a DMM, test for a short between the APP sensor 3 signal circuit and all other TAC module circuits. Did you find and correct the condition? If yes, go to step  25. If no, go to step  21.
  20. Repair the intermittent connection as necessary. After repairs, go to step  25.
  21. Inspect for poor connections at the harness connector of the APP sensor. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  22. Replace the APP sensor assembly. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  25.
  23. Inspect for poor connections at the harness connector of the TAC module. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  24. Replace the TAC module. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to next step.
  25. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  26. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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