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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 >> Cooling Fan Inoperative >> Circuit/System Testing

Circuit/System Testing

IMPORTANT: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
  1. Ignition OFF, disconnect the series/parallel relay.
  2. Ignition ON, activate the cooling fan relay 1 with a scan tool. The fan should be OFF.
    • If the fan is activated, test the left fan ground circuit for a short to ground.
  3. Ignition OFF, disconnect the remaining relays.
  4. Install 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.
  5. One at a time, connect a 30A fused jumper between the positive terminal at the battery and the fan voltage supply circuit terminal at the low speed fan relay and the high speed fan relay connections and verify fan activation.
    • If the appropriate fan does not activate, test the fan voltage supply circuit for a short to ground or open/high resistance. If the circuit tests normal, test the fan ground circuit for an open/high resistance. If the circuits test normal, replace the fan.
  6. Ignition ON, connect a 30A fused jumper between the relay switch voltage supply circuit terminal and the fan voltage supply circuit terminal at the low speed relay and the series/parallel relay connections and verify fan activation.
    • If the fan does not activate, test the 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.
  7. If the circuits and fans test normal, replace the relay.
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