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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1450 (ENGINE COOLING SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P2600-P2603CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6

Circuit/System Testing

2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION 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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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.