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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROL SYSTEM - SELF-DIAGNOSTICS - 4.2LDIAGNOSTIC TESTSDTC P1280: ACCELERATOR PEDAL POSITION CIRCUIT (SENSOR 2)DIAGNOSTIC PROCEDURES
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Diagnostic Procedures

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedures
  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. Turn ignition on, with engine off. With scan tool, observe the APP sensor 2 voltage with the accelerator pedal in the rest position. Does scan tool indicate voltage less than 0.13 volt 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 data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See CONDITIONS FOR RUNNING DTC . Does the DTC fail this ignition cycle? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
  4. Turn ignition off. Disconnect the accelerator pedal harness connector. Turn ignition on, with engine off. With scan tool, observe the APP sensor 2 voltage parameter. Does scan tool indicate voltage at 5 volts? If yes, go to next step. If no, go to step  12.
  5. With a test light connected to ground, probe the APP sensor 2 signal circuit. Does the test light illuminate? If yes, go to step  11. If no, go to next step.
  6. With the test light still connected to the APP sensor 2 signal circuit, observe the APP sensor 2 parameter. Does scan tool indicate voltage at zero volts? If yes, go to next step. If no, go to step  11.
  7. With a DVOM, measure the voltage of the APP sensor 2 5-volt reference circuit. Does the DVOM indicate voltage at 5 volts? If yes, go to next step. If no, go to step  10.
  8. With a test light connected to battery voltage, probe the APP sensor 2 low reference circuit. Does the test light illuminate? If yes, go to next step. If no, go to step  14.
  9. Test the 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 voltage less than 5 volts on the APP sensor 2 5-volt reference circuit? If yes, go to step  14. If no, go to step  16.
  11. Test the APP sensor 2 signal 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  13.
  12. Test the APP sensor 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 the APP sensor 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 the APP sensor 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 the APP sensor 2 5-volt 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 next step.
  16. Test the APP sensor 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 step  20.
  17. Test the APP sensor 2 5-volt reference circuit for a short to voltage. Repair as necessary. After repairs, go to step  22.
  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. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After repairs, go to step  22.
  20. Inspect for poor connections at the PCM harness connector. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  21. Replace PCM. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  22. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  23. Observe the stored information, Capture Info with scan tool. Does 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.