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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 >> DTC P2600-P2603 >> 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 harness connector at the auxiliary coolant pump relay.
    2. IMPORTANT: The ignition circuit supplies voltage to other components. Make sure you test all circuits for a short to ground or test all components for being shorted that share the ignition circuit.
  2. Ignition ON, verify that a test lamp illuminates between the ignition voltage circuit terminal 85 and ground.
    • If the test lamp does not illuminate, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition voltage circuit fuse is open, test all components connected to the ignition voltage circuit and replace as necessary.
    3. IMPORTANT: The control circuit for the auxiliary coolant pump relay is pulled-up to voltage within the ECM, 2.6-4.6 volts on the control circuit is normal.
  3. Test for 2.6-4.6 volts between the control circuit terminal 86 and ground.
    • If less than the specified range, test the control circuit for an open/high resistance or for a short to ground. If the circuit tests normal, replace the ECM.
    • If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Connect a test lamp between the control circuit terminal 86 and the ignition voltage circuit terminal 85.
  5. Command the auxiliary coolant pump relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always OFF, replace the ECM.
  6. If all circuits/connections test normal, test or replace the auxiliary coolant pump relay.
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