Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISBODY & FRAMEWINDOWSFIXED & MOVEABLE WINDOW SYSTEMSDIAGNOSTIC INFORMATION AND PROCEDURESREAR WINDOW DEFOGGER MALFUNCTIONCIRCUIT/SYSTEM TESTINGREAR WINDOW DEFOGGER INOPERATIVE
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Rear Window Defogger Inoperative
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Rear Window Defogger Inoperative
- Ignition OFF, disconnect the X3 harness connector at the HVAC control assembly.
- Test for less than 1 ohm between the ground circuit terminal C and ground
- If greater than the specified range, test for an open/high resistance
- Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal A and ground.
- If the test lamp does not illuminate, test the B+ circuit for an open/high resistance
- Ignition OFF, connect the harness connector at the HVAC control assembly and disconnect the REAR DEFOG relay.
- Test for less than 1 ohm between the ground circuit terminal 85 and ground.
- If greater than the specified range, test for an open/high resistance.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
- If the test lamp illuminates, test the control circuit for a short to voltage.
- Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
- If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
- Ignition ON, connect a 30-A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the rear window defogger grids are activated.
- If the rear window defogger grids do not activate, test the control circuit for an open/high resistance.
- Connect a test lamp between the control circuit terminal 86 and the ground circuit terminal 85.
- Command the rear window defogger grid ON and OFF by pressing and depressing the rear defogger switch. The test lamp should turn ON and OFF when changing between the commanded states.
- If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the HVAC control assembly.
- If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control assembly.
- If all circuits test normal, test or replace the REAR DEFOG relay.
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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.