BREGRET

My 2006 C6 coupe rear widow defogger has stopped functioning. Not a big problem but still..
The shop tells me the electronic module that controls this and the A/C has to be repaired, but GM doesn't offer a replacement part. The module has to be sent out for repair involving weeks. Any one have any experience with this problem?

captain vette

Have you look on EBay or on the used parts market it should not be difficult to find one. Good luck

Landru

No, not that one. Yet.
Have to remember as C6 ages many normally reliable components will surely start failing.
Might find preowned of NOS via Internet, if fact I'd bet on it

Perfect example of this crap in action would be my '08 Z06.
Needed a catalytic converter & O2 sensor.
GM OEM CCs are on national backorder and have been for some time, w/ no availability date whatsoever. Tomorrow? Never?

4SUMERZ

I'm not sure why the HVAC control module can't be replaced. It has the buttons for the AC and Defog functions. These controllers can be purchased pretty much anywhere.
I've attached the Electrical schematic so maybe you can check the fuses/relay to be sure that isn't the issue.
Circuit/System Description
When the rear window defogger switch is activated, the HVAC control module energizes the rear defog relay by grounding the rear defog relay control circuit. When the rear defog relay coil is energized, the switch contacts of the rear defog relay close allowing battery voltage to flow from the BATT 2 fuse through the closed switch contacts and out the relay switched output to the rear window defogger grid. Ground for the rear window defogger grid is provided at G301.

Circuit/System Testing
1. Ignition OFF, disconnect the rear window defog relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal C19 and ground. If the test lamp illuminates, test the control circuit for a short to voltage.
3. Verify that a test lamp illuminates between the relay coil B+ circuit terminal A19 and ground.
If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance.
If the circuit tests normal and the relay coil B+ circuit fuse is open, test or replace the rear defog relay.
4. Verify that a test lamp illuminates between the relay switch B+ circuit terminal A18 and ground.
If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or an open/high resistance.
If the circuit tests normal and the relay coil B+ circuit fuse is open, test the relay controlled output circuit for a short to ground.
5. Ignition OFF, disconnect the C2 harness connector at the rear window defogger grid.
6. Ignition OFF, test for less than 1.0 ohm of resistance between the rear window defogger grid ground circuit terminal A and ground.
If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the C2 harness connector at the rear window defogger grid.
8. Ignition ON, connect a 40 A fused jumper wire between the B+ circuit terminal A18 and the control circuit terminal C19.
Verify the rear window defogger grid is activated.
If the rear window defogger grid does not activate, test the control circuit for an open/high resistance. f the circuit tests normal, test or replace the rear window defogger grid.
9. Connect a test lamp between the B+ circuit terminal A19 and the control circuit terminal C18.
10. Command the rear window defogger ON and OFF with 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 ground. If the circuit tests normal, replace the HVAC control module.
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 HVAC control module.
11. If all circuits test normal, test or replace the rear defog relay.

Component Testing
Rear Window Defogger Grid Test
1. Ignition ON, turn on the rear defogger.
2. Verify that a test lamp illuminates between each rear defogger grid line and ground.
The test lamp should be off when testing at the ground side of the grid and get brighter as the test lamp moves closer to the voltage supply side of the grid.
The test lamp should be dim when testing each grid line in the middle.
If the test lamp remains bright at the middle of a grid line, test for an open between the test point and the ground circuit.
If the test lamp remains off at the middle of a grid line, test for an open between the test point and the voltage supply side of the grid.

Dano523

Keep in mind that the rear defrost will not work until the car is running, but would turn the defrost on with the car running, and look for C18/D19 to be grounded. If you these are grounded through the controller, then the HVAC controller is not the problem.

From there, fuse 29 good, and 12v power to A16/A19.

If good so far, then problem is relay has gone south and just needs to be replaced.

Also, would pull the connectors off the back hatch struts at the bottom, and make sure that you get resistance to ground. Also with the bottom connectors removed from the struts, check the connectors for 12 volts.

Hence the 12 volts to the window grid runs through the struts.

akriggm

When the rear defogger failed in my 2008 coupe a few years back, it was a break in the circuitry in one of the hatch struts......

Enjoy,
akriggm