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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 512 (ENGINE COOLING SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P0483 OR P0493CIRCUIT/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 6 other vehicles, including the 2009 GMC Savana Special, 2009 GMC Savana Camper Special, 2009 GMC Savana, 2009 Chevrolet RV Cutaway, and 2009 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the fan relay.
  2. Measure between the fan relay ground circuit terminal K9 and ground for less than 3 ohms.
    • If more than the specified range, test the ground circuit for an open/high resistance.
  3. Operate the engine at 1,500 RPM for 2 minutes. The fan should be quiet to indicate the clutch is disengaged.
    • If not disengaged, test the cooling fan clutch supply voltage circuit for a short to voltage. If the circuit tests normal, replace the clutch.
  4. Ignition OFF, install a 10A fused jumper wire between the positive terminal at the battery and the cooling fan clutch supply voltage circuit terminal B.
  5. Operate the engine at 1,500 RPM for 2 minutes. The fan should be loud to indicate the clutch is engaged.
    • If not engaged, test the cooling fan clutch supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the clutch.
  6. Ignition OFF, install a 10A fused jumper wire between the relay voltage supply circuit terminal J12 and the cooling fan clutch supply voltage circuit terminal.
  7. Operate the engine at 1,500 RPM for 2 minutes. The fan should be loud to indicate the clutch is engaged.
    • If not engaged, test the relay voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all connected components and replace as necessary.
  8. Connect a test lamp between the positive terminal at the battery and the cooling fan clutch relay control circuit terminal L12.
  9. Engine RUNNING at 1,500 RPM, command the cooling fan clutch to 80 percent for 2 minutes. The test lamp should turn on steady or flash, indicating that the ECM can control the relay.
    • If the lamp does not flash or turn on steady, test the cooling fan clutch control circuit for a short to ground, a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.
    • If the lamp does not flash or vary correctly, test the cooling fan clutch control circuit for a short to ground, a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.
  10. Perform the relay component test. The relay should test normal.
    • If the relay does not test normal, replace the relay.
  11. Ignition OFF, disconnect the fan clutch harness at the shroud.
  12. Measure between the low reference circuit terminal C and ground for less than 3 ohms.
    • If more than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  13. Ignition ON, measure between the 5-volt reference circuit terminal E and the low reference circuit terminal C for 4.8-5.2 volts.
    • If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
    • If more than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  14. Install jumper wires in the 5-volt reference and low reference circuits between the harness and pigtail connectors at the shroud.
    • 5-volt reference circuit terminal E
    • Low reference circuit terminal C
  15. Measure DC voltage between the signal circuit terminal D at the sensor pigtail connector and the 5-volt reference circuit jumper wire terminal.
  16. Ignition ON, rotate the fan by hand. The voltage should toggle between approximately 5 volts and 0 volts.
    • If the voltage does not toggle correctly, test the three circuits in the pigtail harness for a short to ground, a short to voltage, or an open/high resistance. If the circuits test normal, replace the clutch.
  17. Leave the jumpers from the previous step in place. Measure voltage between the signal circuit terminal D of the harness and pigtail connectors at the shroud.
  18. Rotate the fan by hand. The voltage should toggle between approximately 5 volts and 0 volts.
    • If the voltage does not toggle correctly, test the signal circuit for a short to ground, a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.
  19. If all circuits, the relay, and the speed sensor test normal, replace the clutch.
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When to See a Mechanic

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.