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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 942 (Engine Controls And Fuel - 6.6L (LMM) - DTC P154B To DTC P2693) >> DTC P2122, P2123, P2127, P2128, or P2138 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2007 GMC Sierra, 2007 GMC Cab & Chassis Sierra, 2007 Chevrolet Silverado, and 2007 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the harness connector at the APP sensor. Allow at least 60 seconds for the ECM to power down.
  2. Ignition OFF, test for less than 5 ohms of resistance between each low reference circuit terminals A and F, and ground.
    • If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  3. Ignition ON, test for 4.8-5.2 volts between each APP sensor 5-volt reference circuit terminals C and D, and ground.
    • If less than the specified range, test the affected 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
    • If greater than the specified range, test the affected 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Verify that the scan tool APP Sensor 1 and APP Sensor 2 parameters are less than 0.02 volt.
    • If greater than 0.02 volt, test the applicable signal circuit terminals B or E for a short to voltage. If the circuit tests normal, replace the ECM.
  5. Install a 3A fused jumper wire between each signal circuit terminals B or E and the 5-volt reference circuit. Verify that the scan tool APP Sensor parameter is greater than 4.57 volts.
    • If less than the specified range, test the applicable signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
  6. Ignition OFF, disconnect the harness connector at the ECM.
  7. Test for less than 5 ohms of resistance on all APP sensor circuits between the following terminals:
    • The ECM X2 signal circuit terminal 49 to APP terminal E
    • The ECM X1 signal circuit terminal 21 to APP terminal B
    • The ECM X1 5-volt reference circuit terminal 38 to APP terminal C
    • The ECM X2 5-volt reference circuit terminal 15 to APP terminal D
    • If greater than the specified range, repair the affected circuit for open/high resistance.
  8. Test for infinite resistance between APP sensor 1 and 2 signal circuits.
    • If less than infinite resistance, repair the short between signal circuits.
  9. If all circuits test normal, test or replace the accelerator pedal assembly.
    • If the APP sensor tests normal, replace the ECM.
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