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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1284 (Engine Cooling System) >> Diagnostic Information and Procedures >> DTC P0480 or P0481 >> Circuit/System Testing

Circuit/System Testing

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  1. Ignition OFF, disconnect the 3 cooling fan relays listed below.
    • FAN LO relay
    • FAN CNTRL relay
    • FAN HI relay
  2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 85 of each relay and ground.
    • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  3. Verify that a test lamp does not illuminate between the ignition circuit terminal 85 and the control circuit terminal 86 of each relay.
    • If the test lamp illuminates, test the control circuit for a short to ground. If the circuit test normal, replace the ECM.
  4. Remove the test lamp.
  5. Ignition ON, command the affected relay ON using a scan tool. Verify the affected scan tool FC Relay Control Ckt. Short Volts Test Status Parameter is OK.
    • For the FAN LO relay, use the scan tool Fan Relay 1 command.
    • For the FAN CNTRL and FAN HI relays, use the scan tool Relay 2 and 3 command.
    • If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  6. Install a 3A fused jumper wire between the control circuit terminal 86 and the ignition circuit terminal 85. 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.
  7. If all circuits and the ECM test normal, replace the affected relay.
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