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Home >> Pontiac >> 2008 >> Grand Prix GXP >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 3 (Engine Controls And Fuel - 3.8L - Troubleshooting & Diagnosis) >> Malfunction Indicator Lamp (MIL) Diagnosis >> Circuit/System Testing

Circuit/System Testing

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  1. Ignition OFF, disconnect the harness connector at the instrument cluster.
  2. Ignition ON, verify that a test lamp illuminates between the ignition circuit and ground.
    • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test all components connected to the fuse and replace as necessary.
  3. Connect a test lamp between the control circuit and the ignition circuit.
  4. Command the MIL ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the PCM.
    • If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the PCM.
  5. If all circuits test normal, replace the instrument cluster.
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