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Home >> Chevrolet >> 2006 >> Cobalt LTZ >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 13 (Engine Controls - 2.0L - DTC P0351 To DTC P2138) >> Diagnostic Information & Procedures >> DTC P2120, P2122, P2123, P2125, P2127, P2128, or P2138 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different variant/trim than selected.
  1. Clear the DTCs with the scan tool. Operate the vehicle within the Conditions for Running the DTC or within the conditions that you observed from the Freeze Frame/Failure Records.
  2. With the ignition ON, observe the APP sensor 1 voltage parameter with the accelerator pedal in the rest position. The voltage should be between 0.13-4.87 volts.
    • If more than 4.87 volts, test the low reference for an open or a faulty ECM.
    • If less than 0.13 volt, test the APP sensor 1 signal circuit for a short to ground or a faulty ECM.
  3. With the ignition ON, observe the APP sensor 2 voltage parameter with the accelerator pedal in the rest position. The voltage should be between 0.13-4.87 volts.
    • If more than 4.87 volts, test the low reference for an open or a faulty ECM.
    • If less than 0.13 volt, test the APP sensor 2 signal circuit for a short to ground or a faulty ECM.
  4. With the ignition ON, observe the DTCs.
    • If DTC P2120 is the only code set, replace the ECM.
    • If DTC P2125 is the only code set, replace the ECM.
  5. Disconnect the accelerator pedal harness connector and verify APP sensor 1 and 2 voltages are less than 0.1 volt.
    • If more than 0 volts, test the APP sensor 1 and 2 signal circuits for a short to voltage or a faulty ECM.
  6. With the ignition ON, test for 4.8-5.2 volts between both 5-volt reference circuits and the negative terminal of the battery.
    • If more than 5.2 volts, test both 5-volt reference circuits for a short to voltage or faulty ECM.
    • If less than 4.8 volts, test both the 5-volt reference circuits for an open or short to ground or a faulty ECM.
  7. Install a 3-amp fused jumper wire between the signal circuit and the 5-volt reference circuit of the APP sensor 1, and verify the APP 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, short to ground, or a faulty ECM.
  8. Install a 3-amp fused jumper wire between the signal circuit and the 5-volt reference circuit of the APP sensor 2, and verify that the 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, short to ground, or a faulty ECM.
  9. If all circuits test normal, replace the accelerator pedal.

P2138 only

  1. With the ignition OFF, disconnect the accelerator pedal harness connector and the ECM harness connector, and test for less than 5 ohms on each APP sensor circuit.
    • If more than 5 ohms, repair the affected circuit or faulty ECM.
    • If less than 5 ohms, test for a short between APP sensor 1 signal circuit and APP sensor 2 signal circuit.
  2. If all circuits test normal, replace the accelerator pedal.
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