Can anyone offer any insight into troubleshooting the heated outside mirrors on a '99 V70XC? Today was our first real frost and everything was coated in frost / ice. I started up the car, set the front and rear defroster, waited a few minutes and the front and rear windows cleared nicely, the passenger side outside mirror was clear and warm to the touch, the drivers side outside mirror was cold and frosty. Is this typically a glass replacement, whole mirror assy replacement, or maybe just a fuse. Honestly, I guess it could be that simple. In the car I thought the fuse must be ok but while typing I just thought, I wonder if it is fuse(s) and maybe one of two are bad, hmmmm? Any ideas if the mirrors are on a single fuse or what to check?

I actually did try searching before posting this question.

Thanks,
Don
Billings MT
'99 V70XC

 

First time I've seen the question on any model. I would check the plug for power with the door closed just in case the wire harness going through the door has a broken wire.

 

I looked in the book and it mentions rear demister and heated mirrors for fuses 14 and 29. On the label on the underside of the fuse panel it only mentions heated mirrors on one of those, the other says power mirrors I think. Anyway, both fuses are good. I pulled the triangle shaped panel inside the door (which easily pulls straight out) and saw the wire but not the plug. The power adjustment of the mirror works fine, just not heat.

Is the plug in the mirror or behind the door panel?

 

Behind the door panel. The wires go from the mirror and into the door about 14 inches.
Door Panel Removal for Volvo 850 - Mirror Replacement

 

So in reading more about 70 series mirrors, not necessarily the heat function, I discovered that the glass can be removed without removing the door panel or the mirror housing.

I don't have pics but I did find a site that showed replacement glass and a picture of the front and back. From the pic I knew I was looking for wires that simply plug into the back of the glass. Also, there is about a three inch circle that has 8 clips around it. Simply use a flat blade screwdriver to slip between the glass and the housing on each side and the glass and plastic backing (attached to the glass) will pop right out.

There are two wires to the back of the glass supplying 12V when the rear demist (defog) and heated mirrors are activated. The Black wire goes on the bottom (although for a DC heated device I doubt it matters) and the colored wire goes on top.

Also check resistance across the terminals on the back of the mirror. it should read about 8 ohms.

I took my defunct mirror off and it read over 10M ohms. Well to start with I had no idea what it should be so i took off the other mirror and checked for 12V from the plugs and the mirror's resistance. When I read 8 ohms on the working one I knew right away that my other one with over 10M ohms was bad.

I will begin the search for a replacement glass and I'm sure this will cure my problem. Now I know to take my meter with me to the scrap yard and what to look for. I hope this helps anyone who is troubleshooting heated mirrors.

Don
Billings MT
'99 V70XC