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Home >> Hummer >> 2008 >> H2 4D Utility Wagon >> Repair and Diagnosis >> Engine Mechanical >> Cooling System (Mechanical) >> Engine Cooling >> Diagnostic Information and Procedures >> DTC P0480 or P0481 >> Circuit/System Testing

Circuit/System Testing

  1. Ignition OFF, disconnect the series/parallel relay, which is the FAN CNTRL relay.
  2. Connect a 30A fused jumper between the normally-open switch contact terminals at the series/parallel relay connector in order to complete the fan ground circuit. Leave this jumper in place for the remainder of this procedure.
  3. Ignition OFF, disconnect the affected relay.
  4. Verify that a test lamp does not illuminate between B+ and the affected relay control circuit terminal.
  5. Remove the test lamp.
  6. Command the affected relay ON with a scan tool. Verify the scan tool Relay Control Ckt. Short Volts Test Status Parameter is OK.
    • If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  7. Install a 3A fused jumper wire between the control circuit terminal and B+. Command the affected relay ON with a scan tool. Verify the scan tool Relay Control Ckt Short Volts Test Status Parameter is Fault.
    • If not the specified value, test the control circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  8. Remove the 3A fused jumper wire.
  9. Connect a 30A fused jumper between the positive voltage terminal at the battery and the fan voltage supply circuit terminal at the affected relay connector and verify fan activation.
    • If the fan does not activate, test the fan voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the fan.
  10. Ignition ON, connect a 30A fused jumper between the relay switch voltage supply circuit terminal and the fan voltage supply circuit terminal at the affected relay connector and verify fan activation.
    • If the fan does not activate, test the affected relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.
  11. Ignition ON, verify that a test lamp illuminates between the affected relay coil voltage supply circuit terminal and ground.
    • If the test lamp does not illuminate, test the affected relay coil voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.
  12. If all circuits and the ECM test normal, replace the affected relay.
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