Rear defrost does not work

[Trey]

My rear defrost does not work. Note that the light on the button turns on and I can hear the relay activate but the passengers footwell, but something is going wrong because the fog will not go away. I have checked fuse 19 and fuse 2, and both are OK. I can hear the relay click - so I assume the relay is OK. Does anyone have any advice?

[Trey]

Also, my wipers and door locks both work.

[NCReatta]

Any broken lines on the glass?

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[Corvanti]

probably a broken "grid line" on the window. but maybe no power or ground on the bus lines... check if there's an obvious break in the grid line - the wires that run in the glass. repair kits are available at most "flaps" (Friendly Local Auto Parts Store).

if you have a service manual, it's on page 10-2-7. (final edition 1988 service manual). if you don't have a service manual, get one!

[Trey]

I forgot to mention that I have an active B123 code. I am looking that up in my 1988 service manual.

[Trey]

I do not see any cracks in the grid.

[rjfranken]

All of mine have the entire conducting strip on one side seperated from the glass where the connector is glued on. I have been looking for conductive epoxy or nickel metal paint to repair this. Not having much luck though.

[Mc_Reatta]

Bob, Adhesive that holds grid to glass doesn't have to be electrically conductive. Needs to be thin to conduct the heat to the glass.

If you get a kit to repair a rear window defroster, some will come with the conductive paint used to repair a gap in the grid, and with a heaver adhesive to attach the two contacts at the bottom center of the grid to the glass where the wires from the car come up and attach.

Just use one of those to reattach the grid to the glass. Use the paint sparingly if its just the light grid that needs to be reattached, and the heavier adhesive where there is more stress on the grid. If you get too much oozing out of the repair, use a razor blade to scrape off the excess.

[Trey]

My wires are still attached and all the grid lines look to be intact - could it be a relay or fuse issue?

[Corvanti]

it could be a fuse or relay, but i think earlier you said they were ok.

start from the rear defroster - if you don't have one, get one of these:

Motormite/Conduct-Tite! 6 and 12 Volt DIY circuit tester with power on (86599) | Circuit Tester | AutoZone.com

...and check if you have power to the connections - both positive and ground sides. then go forward in the wiring - to the relay, fuse, etc...

hope this helps.

[Trey]

Thanks - I will try that. About the relay, is it possible that it makes a noise but is still broken?

[Mc_Reatta]

The Rear Defogger is a complicated circuit. Fuse block Wiper fuse #12 supplies voltage to the switch in the right side pod. Does the light in the switch come on when switch is activated?

Then that signal goes to the IPC which sends a signal out over the data line to the BCM which relays it on to the HVAC Programmer.

The Programmer interprets the data signal and grounds relay "D" in the Interior Relay Center which is powered via fuse block AC fuse #19.

This relay then supplies power supplied by Interior Relay Center Defogger fuse #2 to the rear defogger and the heated drivers side view mirror. Need to remove console passenger side cover to get to this fuse and relay.

So you have 3 fuses, 2 switches 1 relay and 3 modules all to get 12 volts back to the rear window defogger grid. (Don't forget the splices and connectors involved with all the internal wiring either)

Kind of makes you wonder how it worked in the first place.

[Trey]

I put a volt meter on the two wires on the rear window and I am getting twelve volts when the button is pushed (the light on the button does light up). However, the fog does not go away. What could be wrong?

[Trey]

Update - I covered the sharp points of the voltmeter probes with tin foil and tested all of the painted lines. They all showed twelve volts except for the top two. Should my rear defrost be mostly working - or do they all have to work to have a functioning rear defrost?

[Barney Eaton]

Did you get a car with the "Houston fog" option? It sounds like it should be working.......maybe you are expection it to work quicker than it does (with Houston fog)

[Trey]

It seems like normal fog to me. In my saturn, the back window will clear up pretty soon, but no effect at all in the Reatta. It is really strange.