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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 87 (Engine Controls - Self-Diagnostics - 6.6L Diesel) >> Diagnostic Tests >> DTC P1271: App Sensor 1-2 Performance >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  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. Observe the Freeze Frame/Failure Records data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC or as close to the Freeze Frame/Failure Records data that you observed. Does the DTC fail this ignition cycle? If yes, go to step  4. If no, go to next step.
  3. Select the Diagnostic Trouble Code (DTC) option using the scan tool. Lightly touch and move the related APP wiring harnesses and connectors while monitoring the DTC Information. Did this DTC fail this ignition cycle, during the above test? If yes, go to next step. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  4. Is DTC P1272 also set? If yes, go to step  6. If no, go to next step.
  5. Is DTC P1273 also set? If yes, go to step  9.
  6. Turn OFF the ignition. Disconnect the APP sensor harness connector. Turn ON the ignition. With a test lamp connected to ground, test for voltage at the APP sensor 2, 5-volt reference circuit. Does the test lamp illuminate? If yes, go to next step. If no, go to step  13.
  7. With a test lamp connected to ground, test for voltage at the APP sensor 2 signal circuit. Does the test lamp illuminate? If yes, go to next step. If no, go to step  14.
  8. Connect a test lamp between the APP sensor 2, 5-volt reference circuit and the APP sensor 2 low reference circuit. Does the test lamp illuminate? If yes, go to step  18. If no, go to step  15.
  9. Turn OFF the ignition. Disconnect the APP sensor harness connector. Turn ON the ignition. With a test lamp connected to ground, test for voltage at the APP sensor 1, 5-volt reference circuit. Does the test lamp illuminate? If yes, go to next step. If no, go to step  16.
  10. Connect the test lamp between the APP sensor 1, 5-volt reference circuit and the APP sensor 1 low reference circuit. Does the test lamp illuminate? If yes, go to next step. If no, go to step  17.
  11. Connect a fused jumper wire between the APP sensor 1 signal circuit and the APP sensor 1, 5-volt reference circuit. With a scan tool, observe the APP sensor 1 voltage parameter. Does the scan tool indicate voltage at 5 V? If yes, go to step  18. If no, go to next step.
  12. Turn OFF the ignition. Disconnect the ECM harness connector that contains the APP sensor 1 signal circuit. With a Digital Multimeter (DMM), test the APP sensor 1 signal circuit for high resistance. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  13. Turn OFF the ignition. Disconnect the ECM harness connector that contains the APP sensor 2, 5-volt reference circuit. With a DMM, test the APP sensor 2, 5-volt reference circuit for high resistance. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  14. Turn OFF the ignition. Disconnect the ECM harness connector that contains the APP sensor 2 signal circuit. Turn ON the ignition. With a DMM, test the APP sensor 2 signal circuit for high resistance. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  15. Turn OFF the ignition. Disconnect the ECM harness connector that contains the APP sensor 2 low reference circuit. With a DMM, test the APP sensor 2 low reference circuit for resistance. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  16. Turn OFF the ignition. Disconnect the ECM harness connector that contains the APP sensor 1, 5-volt reference circuit. Turn ON the ignition. With a DMM, test the APP sensor 1, 5-volt reference circuit for high resistance. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  17. Turn OFF the ignition. Disconnect the ECM harness connector that contains the APP sensor 1 low reference circuit. With a DMM, test the APP sensor 1 low reference circuit for resistance. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  18. Inspect for poor connections at the harness connector of the APP sensor. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  19. Replace the APP sensor assembly. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  22.
  20. Inspect for poor connections at the harness connector of the ECM. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  21. Replace the ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram ECM. See ENGINE CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  22. 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.
  23. 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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