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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1136 (Engine Cooling System) >> Diagnostic Information and Procedures >> Cooling Fan Inoperative >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the cooling fan relays.
  2. Connect a 30A fused jumper between the relay switch circuit terminal 30 and the ground circuit terminal 87 at the series/parallel fan 2 relay connector. This will complete the left side fan ground circuit. Leave this jumper in place for the remainder of this procedure.
    3. IMPORTANT: The following test must be performed on both the high speed fan 3 relay circuit and the low speed fan 1 relay circuit.
  3. Ignition ON, verify that a test lamp illuminates between the relay switch ignition circuit terminal 30 and ground.
    • If the test lamp does not illuminate, test the appropriate relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the relay.
    4. IMPORTANT: The following test must be performed first on the high speed fan 3 relay circuit and next on the low speed fan 1 relay circuit. Leave the jumper connected to the low speed fan relay circuit for the next test.
  4. Connect a 30A fused jumper between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87. Verify the appropriate fan is activated
    • If the appropriate fan does not activate, test the relay controlled output circuit for a short to ground or an open/high resistance. If the circuit tests normal, test the fan ground circuit for an open/high resistance. If the circuit tests normal, replace the fan.
  5. Install the series/parallel fan 2 relay. Verify both fans activate at low speed.
    • If both fans do not activate, test the relay controlled output circuit terminal 87A of the series/parallel fan 2 relay for a short to ground or an open/high resistance.
  6. If all circuits test normal, test or replace the relay.
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