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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 332 (HVAC SYSTEM - AUTOMATIC)DIAGNOSTIC INFORMATION AND PROCEDURESDTC B3844CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G3500, Van Passenger Extended

Circuit/System Testing

2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
  1. Disconnect the heater core coolant pump relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit terminal 87 and ground.
    • If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.
    • If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay coil 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 heater core coolant pump relay.
  4. Verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.
    • If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance.
  5. Disconnect the harness connector at the heater core coolant pump.
  6. Test for less than 5.0 ohms between the heater core coolant pump ground circuit terminal and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the heater core coolant pump.
  8. Connect a 15 A fused jumper wire between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87. Verify the heater core coolant pump is activated.
    • If the heater core coolant pump does not activate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the heater core coolant pump.
  9. Connect a test lamp between the relay coil B+ circuit terminal 85 and the relay coil control circuit terminal 86.
  10. Command the heater core coolant pump 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 ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the HVAC control module.
    • If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  11. If all circuits test normal, test or replace the relay.
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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