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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 51 (Engine Control System - Self-Diagnostics - 4.2L) >> Diagnostic Tests >> DTC P1271: Excessive Difference Between Accelerator Pedal Position Sensors >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. 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. Using a scan tool, observe the DTC information. Is DTC P1120, P1220, P1275, P1280, P1635, or P1639 also set? If yes, see DTC P1120: TP SENSOR CIRCUIT  , DTC P1220: THROTTLE POSITION SENSOR 2 - LOW VOLTAGE  , DTC P1275:  , DTC P1280:  , DTC P1635: 5-VOLT REFERENCE A CIRCUIT  or DTC P1639: 5-VOLT REFERENCE B CIRCUIT  . If no, go to next step.
  3. Turn OFF the ignition. Disconnect the APP sensor electrical connector. Disconnect the PCM. Use a Digital Multimeter (DMM) to measure the resistance of the following circuits for each of the APP sensors:
    • The low reference circuit.
    • The signal circuit.
    • The 5-volt reference circuit.

    Did any of the circuits measure more than 5 ohms? If yes, go to step  5 . If no, go to next step.

  4. Test for a short between any of the circuits in the APP sensor harness. Repair the circuit as necessary. Did you find and correct the condition? If yes, go to step  7 . If no, go to step  6 .
  5. Repair the high resistance in the circuit. After repairs, go to step  7 .
  6. Replace the APP sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to next step.
  7. 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 .
  8. 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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