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BigBlock434, Chevy Mechanic
Category: Chevy
Satisfied Customers: 291
Experience:  ASE Master certified and 100% General Motors trained in all fields
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2005 chevy cobalt: rear defrost..doesnt work..the relay but nothing

Customer Question

i have a 2005 chevy cobalt and the rear defrost doesnt work? there is power to the switch and to the relay but nothing to the back of the car, any i deas of what the problem is?
Submitted: 7 years ago.
Category: Chevy
Expert:  BigBlock434 replied 7 years ago.
OK I am assuming you checked the power connector at the defogger grid that is how you know you have no power to the grid. Does the light light up when push the deffogger switch? If it does then we know the switch and ground to switch is good. If it doesn't pull HVAC control module and check for a good ground at connector two(black eight pin. Remember there are two black eight pin connectors on the HVAC module) terminal A5. If ground is good check switch operation. Go to Body Control Module(located in passanger floor board left side. Locate connector two(grey 72 pin connector. Again there are two). Find pin 68. While activating switch see if you have a ground there. If so your switch is good if not replace switch. Locate connector one(grey 72 pin) pin 16 white wire. See if you have power there when activating switch. If you don't the BCM is bad. If so then go to under hood fuse block, locate rear deffogger relay activate switch and see if relay clicks. If it doesn't pull relay and check for switch power at connector two White wire terminal F1. If you don't you have a open in white wire between BCM and under hood fuse block. If you do check for battery power at one of the terminals of the relay. If you don't have power then check fuse to see if it has power. If fuse has power then replace under hood fuse block. if all is OK see if there is another relay that has the same number, switch relays and see if deffogger works. If it doesn't Check ground on connector two of underhood fuse panel terminal A(Light grey 68 pin connector. If ground is good ohm wire connector two of the under hood fuse block connector two pin E1 to rear deffogger grid for open.
Expert:  BigBlock434 replied 7 years ago.
Defogger Schematics
Object Number:(NNN) NNN-NNNN Size: FS