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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 181 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 2.2L)DIAGNOSTIC TESTSDTC P1280: ACCELERATOR PEDAL POSITION SENSOR 2 CIRCUITDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedures

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. Turn ignition on, with engine off. Observe the APP sensor No. 2 voltage with the accelerator pedal in the rest position with a scan tool. Does the scan tool indicate that the voltage is less than 0.13 volts or greater than 4.87 volts? If yes, go to step  5. If no, go to next step.
  3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 90 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 2.2L & 3.0L VUE article.
  4. Turn ignition off. Disconnect the accelerator pedal harness connector. Turn ignition on, with engine off. Observe the APP sensor No. 2 voltage parameter with a scan tool. Does the scan tool indicate that the voltage is greater than 4.8 volts? If yes, go to next step. If no, go to step  12.
  5. Probe the APP sensor No. 2 signal circuit with a test light connected to ground. Does the test light illuminate? If yes, go to step  12. If no, go to next step.
  6. Observe the APP sensor 2 parameter with the test light still connected to the APP sensor No. 2 signal circuit. Does the scan tool indicate that the voltage is less than 0.13 volt? If yes, go to next step. If no, go to step  11.
  7. Measure the voltage of the APP sensor No. 2 5-volt reference circuit with a DVOM. Does the DVOM indicate that the voltage is greater than 4.8 volts? If yes, go to next step. If no, go to step  10.
  8. Turn ignition off for 90 seconds. Allow the ECM to completely power down. This can be verified by the loss of communication on the scan tool. Measure the resistance from the low reference circuit of the APP sensor to the ECM case with the DVOM. Is the resistance less than 5 ohms? If yes, go to next step. If no, go to step  14.
  9. Test APP sensor low reference circuit for a short to ground. Did you find and correct the condition? If yes, go to step  22. If no, go to step  18.
  10. Does the DVOM indicate that the voltage is less than 5 volts on the APP sensor No. 2 5-volt reference circuit? If yes, go to step  14. If no, go to step  15.
  11. Test APP sensor No. 2 signal circuit for an open or for high resistance. Did you find and correct the condition? If yes, go to step  22. If no, go to step  13.
  12. Test APP sensor No. 2 signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  13. Test APP sensor No. 2 signal circuit for a short to ground. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  14. Test APP sensor No. 2 low reference circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  15. Test APP sensor No. 2 5-volt reference circuit for an open or for high resistance. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  16. Test APP sensor No. 2 5-volt reference circuit for a short to ground. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  17. Test APP sensor 2 5-volt reference circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  18. Inspect for poor connections at the accelerator pedal harness connector. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  19. Replace accelerator pedal assembly. After replacing the accelerator pedal assembly, go to step  22.
  20. Inspect for poor connections at the ECM harness connector. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  21. Turn ignition off. Replace ECM. Perform ECM relearn procedure. See ELECTRONIC CONTROL MODULE REPROGRAMMING  under PROGRAMMING. After replacing ECM, go to next step.
  22. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See CONDITIONS FOR RUNNING DTC . You may also operate vehicle within the conditions observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step  2. If no, go to next step.
  23. With a scan tool, observe the stored information, Capture Info. 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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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.