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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 400 (HVAC SYSTEM - AUTOMATIC)DIAGNOSTIC INFORMATION AND PROCEDURESBLOWER MOTOR MALFUNCTIONCIRCUIT/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 is about a different car, the 2009 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the BLOWER relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground.
    • If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the B+ circuit terminal 87 and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the BLOWER fuse is open, test the B+ circuit for a short to ground. If the circuit tests normal, replace the blower controller.
  4. Connect a test lamp between the control circuit terminal 86 and B+.
  5. Command the blower motor ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
    • If test lamp is always ON, test for short to ground. If circuit tests normal, replace the blower relay.
  6. Connect the BLOWER relay.
  7. Ignition OFF, disconnect the X2 harness connector at the blower controller.
  8. Test for less than 1 ohm between the ground circuit terminal 5 and ground.
    • If not the specified range, test the ground circuit for an open/high resistance.
  9. Connect a test lamp between the B+ circuit terminal 6 and ground.
  10. Turn ON the blower motor. Verify the test lamp illuminates.
    • If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If the circuit tests normal, test or replace the BLOWER relay.
  11. Install a test lamp between the control circuit terminal 3 and B+.
  12. Turn the blower motor ON and cycle between low and high speeds. The test lamp should dimly illuminate at high speeds and reduce in intensity as the blower speed is reduced.
    • If the test lamp does not illuminate, test the control circuit for short to voltage or an open/high resistance. If the circuits test normal, test or replace the HVAC control module.
    • If the test lamp does not change intensity, test the control circuit for a short to ground. If the circuit tests normal, test or replace the HVAC control module.
  13. Connect the harness connector at the blower controller.
  14. Disconnect the harness connector at the blower motor.
  15. Install at test lamp between the B+ circuit terminal 2 and ground.
  16. Turn ON the blower motor. Verify the test lamp illuminates.
    • If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  17. Install a test lamp between the control circuit terminal 1 and the B+ circuit terminal 2.
  18. Turn the blower motor ON and cycle between low and high speeds. The test lamp should illuminate and change in intensity as the blower speed is varied.
    • If the test lamp does not illuminate, test the low reference circuit for short to voltage or an open/high resistance. If the circuit tests normal, test or replace the blower controller.
    • If the test lamp does not change intensity, test the low reference circuit for a short to ground. If the circuit tests normal, test or replace the blower controller.
  19. If all circuits test normal, test or replace the blower motor.
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