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Home >> GMC >> 2006 >> Envoy 4.2 S, 4WD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - 4.2L - DTC P0135 To P0418 >> DTC P0412 >> Circuit/System Testing

Circuit/System Testing

  1. With the ignition ON, the engine OFF, and the solenoid enabled with a scan tool, observe the relay and the solenoid while manipulating all related wiring and connectors.
    • If manipulation does affect the relay or the solenoid, repair the harness or connector.
  2. With the ignition ON, the engine OFF, and the solenoid relay removed, connect a test lamp from the relay coil voltage supply circuit to ground and observe that the lamp illuminates.
    • If the lamp does not illuminate, test the voltage supply circuit for high resistance or a short to ground.
  3. With the ignition ON, the engine OFF, and the solenoid relay removed, connect a test lamp from the relay coil voltage supply circuit to the relay control circuit and observe that the lamp does not illuminate.
    • If the lamp illuminates, test the control circuit for a short to ground or a faulty control module.
  4. With the ignition ON, the engine OFF, the solenoid relay removed, a test lamp connected from the relay coil voltage supply circuit to the relay control circuit, and the AIR solenoid enabled with a scan tool, observe that the test lamp illuminates.
    • If the lamp does not illuminate, test the relay control circuit for high resistance, a short to voltage, or a faulty control module.
  5. If all circuits and the control module are OK, replace the solenoid relay.
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