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Home >> Chevrolet >> 2008 >> Optra LS, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls And Fuel - 2.0L (Diesel) >> Diagnostic Information and Procedures >> DTC P2120, P2125, or P2138 >> Circuit/System Testing

Circuit/System Testing

  1. Ignition OFF, and the MAIN fuse removed, disconnect the harness connector at the accelerator pedal assembly.
  2. Test for less than 5 ohms of resistance between the appropriate low reference circuit and ground.
    • APP Sensor 1 low reference circuit terminal 4
    • APP Sensor 2 low reference circuit terminal 2
    • If greater than the specified range, test the low reference circuit for a short to voltage, or an open/high resistance. If the circuits test normal, replace the ECM.
    3. IMPORTANT: The 5-volt reference circuits are internally and externally connected at the ECM. Other component DTCs may be set. If other DTCs are set, review the electrical schematic and diagnose the applicable circuits and components.
  3. Install the MAIN fuse. Ignition ON, test for 4.8-5.2 volts between the appropriate 5-volt reference circuit and ground.
    • APP Sensor 1 5-volt reference circuit terminal 5
    • APP Sensor 2 5-volt reference circuit terminal 6
    • If less the specified range, test the 5-volt reference circuit for a short to ground or open/high resistance. If the circuits test normal, replace the ECM.
    • If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuits test normal, replace the ECM.
  4. Verify the appropriate scan tool APP sensor parameter is less than 0.3 volt.
    • APP Sensor 1 signal circuit terminal 3
    • APP Sensor 2 signal circuit terminal 1
    • If greater than the specified range, test the appropriate signal circuit for a short to voltage. If the circuits test normal, replace the ECM.
  5. Install a 3A fused jumper wire between the appropriate signal circuit and the 5-volt reference circuit. Verify the scan tool APP sensor parameter is greater than 4.8 volts.
    • If less than the specified range, test the appropriate signal circuit for a short to ground or an open/high resistance. If the circuits test normal, replace the ECM.
    • If both scan tool APP sensor parameters display greater than the specified range, test the signal circuits for being shorted together condition. If the circuits test normal, replace the ECM.
  6. If all circuits test normal, replace the accelerator pedal assembly.
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