Rear window defogger failure on my 04 C2 Cab

[MikeA]

My rear window defogger on my 04 C2 Cab does not appear to be working. The light on the switch does not come on when turned on. It appears as if the side mirror defoggers as well as rear window defogger do not heat up but it is hard to tell. It is the same with hardtop rear window as well. Unlikely that both the ragtop and hardtop would have failed heating elements so it is probably something else. I have checked the fuse box and all the fuses are OK.

Does anyone have any ideas on how I can troubleshoot the problem? I hate to take my car to the dealer for these minor things but it bothers me that it does not work on a car that is less than a year old.

Thanks

Mike

[Loren]

Does the light on the switch go on when you push it?

They all share a control unit for power and control.

[MikeA]

Does the light on the switch go on when you push it?

They all share a control unit for power and control.

<{POST_SNAPBACK}>

Nope... the light does not come on.

[Loren]

Changed anything in the dash recently (like the radio etc.)? If so, you may have knocked a wire off - if not, you could have a bad control unit.

[MikeA]

No changes of any type other than the hardtop mounting hardware in the back of the car. Loren, do you think it is possible that when I plugged the wire from the hardtop mounting bracket into the plug on the cars wiring harness that it could have caused the control unit to fail? I would have thought that any short in the wiring would have been protected by a fuse. The fuse for the defogger is OK. I checked it with an ohm meter for continuity. Where is the control unit? Is there a way to test it or is it easily replaced? Also as I mentioned, I have disconnected the wire from the hardtop bracket to the car's plug for the defogger and eliminated the hardtop wiring from the car. The defogger still does not come on.

Thanks

Mike

[Loren]

Check relay 4 (top row fourth relay from the left).

[MikeA]

How do I check the relay? Is there a simple way to see if the relay is woring or not?

Thanks

[Loren]

Well, most of the relays I have opened were not really relays in the traditional sense - they were digitial switching circuits. So, you may have to swap it out with another relay with the same part number - from someone else's car to be sure.

[Scouser]

Are you taliking about the rear window in the cab top?

Just a hunch, it could be bad connection in the top locating pins. Try lifting the top and replacing it.

[MikeA]

Well, most of the relays I have opened were not really relays in the traditional sense - they were digitial switching circuits.  So, you may have to swap it out with another relay with the same part number - from someone else's car to be sure.

<{POST_SNAPBACK}>

Once I found the relay I pushed on it and determined that it was not fully seated on the socket. After pushing it in completely the defogger works fine. Looks like it was just a partly unplugged relay that caused the whole thing. Funny how I only noticed it after I completed the hardtop install.

As always, thanks Loren and everyone else for your suggestions.

Mike