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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 2306 (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 2010 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
    NOTE: The UBEC label may refer to this relay as the ENG PUMP or FUEL COOL relay.
  1. Ignition OFF, disconnect the harness connector at the KR31 auxiliary coolant pump relay.
    2. NOTE: 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. NOTE: 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. Connect the red lead of the DMM to the KR31 relay control circuit terminal 86. Connect the black lead to ground. Set the DMM to the diode test setting. The DMM should display OL.
    • If less than the specified range, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the K20 ECM.
  4. Command the auxiliary coolant pump relay ON and OFF with a scan tool. The DMM should transition from OL when commanded OFF to less than 1 V when commanded ON.
    • If the circuit voltage does not correspond to the specified values, test the control circuit for an open/high resistance or for a short to voltage. If the circuit tests normal, replace the K20 ECM.
  5. If all circuits/connections test normal, test or replace the KR31 auxiliary coolant pump relay.
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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