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 MANUALSCHEVROLET2008UPLANDER LT, 3.9 1REPAIR AND DIAGNOSIS (SINGLE PAGE)ACCESSORIES & EQUIPMENTHEATED GLASS/DEFOGGERSFIXED & MOVEABLE WINDOW SYSTEMSDIAGNOSTIC INFORMATION AND PROCEDURESREAR WINDOW DEFOGGER MALFUNCTIONCIRCUIT/SYSTEM TESTING
2008 Chevrolet Uplander LT, 3.9 1
Circuit/System Testing
2008 Chevrolet Uplander LT, 3.9 1SECTION Circuit/System Testing
- Ignition OFF, disconnect the RR DEFOG relay.
- Ignition ON, verify that a test lamp does not illuminate between the coil side control circuit terminal and ground.
- If the test lamp illuminates, test the control circuit for a short to voltage.
- Verify that a test lamp illuminates between the coil side B+ terminal 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 B+ circuit fuse is open, test or replace the RR DEFOG relay.
- Verify that a test lamp illuminates between the switch side B+ terminal 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 B+ circuit is open, test the control circuit terminal switch side control for a short to ground.
- Disconnect the harness connector C1 at the rear window defogger grid.
- Test for less than 1 ohm of resistance between the rear window defogger ground circuit terminal C2 and ground.
- If greater than the specified value, test the ground circuit for an open/high resistance.
- Connect the harness connector at the rear window defogger grid.
- Connect a 40-amp fused jumper wire between the switch side B+ terminal and the switch side control terminal. Verify the rear window defogger is activated.
- If the rear window defogger does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the rear window defogger grid.
- Connect a test lamp between the coil side B+ terminal and the coil side control terminal.
- Command the rear window defogger 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 control circuit for a short to ground. If the circuit tests normal, replace the BCM.
- 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 BCM.
- If all circuits test normal, test or replace the RR 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.