Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
Hi and thank you for your question, It looks like you are on the right path. Power comes from the HVAC control module to the under hood fuse box, through the REAR DEFOGGER relay, then through the 40 amp BATT3 fuse, check that fuse. If it's blown, replace it. If the fuse is good, proceed with a volt meter or lighted circuit tester to the connector directly on the back glass. If there is power (12v) or if your test light lights, there is sufficient power to the grid. That would tell you the rear defogger grid is open electronically. If there is no power to the back glass, you'll have to trace the wiring from the back glass forward to the fuse box. I hope this helps.