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Home >> GMC >> 2006 >> Sierra 1500 HD, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1052 (Engine Controls And Fuel - 4.3L - DTC P0340 To DTC P2138) >> DTC P2120, P2122, P2123, P2125, P2127, P2128, or P2138 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2008 GMC Sierra and 2008 Chevrolet 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 accelerator pedal. Allow sufficient time for the ECM to power down.
  2. Test for less than 5 ohms between each low reference circuit terminals A and F and ground.
    • If greater than 5 ohms, 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 5-volt reference circuit terminals D and C and ground.
    • If less than 4.8 volts, test the affected 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
    • If greater than 5.2 volts, test the affected 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Ignition ON, verify the scan tool APP sensor 1 and 2 voltages are less than 0.1 volt.
    • If greater than 0.1 volt, test the APP sensor 1 and 2 signal circuits terminals E and B for a short to voltage. If the circuit tests normal, replace the ECM.
  5. Install a 3A fused jumper wire between the signal circuit terminal E and the 5-volt reference circuit terminal 2 of the APP sensor 1. Verify the scan tool parameter AP sensor 1 voltage is greater than 4.8 volts.
    • If less than 4.8 volts, test the APP sensor 1 signal circuit for an open, or short to ground. If the circuit tests normal, replace the ECM.
  6. Install a 3A fused jumper wire between the signal circuit terminal B and the 5-volt reference circuit terminal 1 of the APP sensor 2. Verify that the scan tool parameter APP sensor 2 voltage is greater than 4.8 volts.
    • If less than 4.8 volts, test the APP sensor 2 signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
  7. Ignition OFF, disconnect the harness connector at the ECM.
  8. Test for less than 5 ohms on all APP sensor circuits between the following terminals:
    • ECM X1 signal circuit terminal 1 to APP terminal E
    • ECM X1 signal circuit terminal 18 to APP terminal B
    • ECM X1 5-volt reference circuit terminal 47 to terminal D
    • ECM X1 5-volt reference circuit terminal 67 to terminal C
    • If greater than 5 ohms, repair the affected circuit.
  9. Test for infinite resistance between APP sensor 1 signal circuit terminal E and APP sensor 2 signal circuit terminal B.
    • If less than infinite resistance, repair the short between APP sensor 1 signal circuit and APP sensor 2 signal circuits.
    • If all circuits test normal, replace the accelerator pedal.
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