Volvo UEM rear view mirror repair.

 Just as I thought that my Volvo can't surprise me anymore it comes around and does it yet again. But I persist and I will not back down to pain in the ass engineering. Each day this car presents me with new challenges and so I will make the most of them by turning them into content for this blog. So what is it this time you ask? Simple, the rear view mirror tinting fluid leaked and turned it into a lava lamp. I mean, how bad can it be? Just buy a replacement and replace it. It's just a mirror right? Riiiiight??? 

Foreshadowing aside, I went head first into this problem with a replacement mirror for 20€. And without suspecting any funny business started tearing the interior apart. Pulling this mirror off was quite simple. The plastic trim over the lights comes off with just a few clips and after that a pair of M6 bolts and a handful of springy retainers are all that hold the light assembly and the rear view mirror in place. After this, a T30 torx is needed to undo the single screw holding the mirror in place and then the mirror can be freed. Before pulling too hard on the mirror you need to disconnect the cable and it's done by inserting a blunt object into the hole at the bottom of the mirror to depress the connector lock and release the connector. Which is a pretty big connector for what it's worth. Geez it's just a mirror, calm down Volvo. 

*narrator voice* - "It was not just a mirror"

Okay so out with the old and in with the new-ish. The replacement fit just the same as the old mirror as it is the same thing basically, but reattaching the light assembly is a massive pain in the rear. Somehow cables keep getting in between the mounting surfaces and prevent the assembly from seating in fully. So after a lot of tugging I was able to get it in all the way. Geez that was easy, all things considered, I guess I'll test it out real quick and see if it works before buttoning it all up....... And it doesn't. In fact nothing works anymore. My keyfob doesn't work anymore and what's worse is that the sunroof switch doesn't work at all. You might say that I can live without a sunroof. Yeah that would be ok had I not left it fully open.

First instinct is to hit the ole reliable google and see what people have going on and they say that there's a Volvo upper electronic module up there, which can get wacky and a restart helps bring it back around. Ok, so I did the konami code to reset the UEM and it didn't help. To make sure I did it a couple more times and it's still not working. Internet also says that pulling on the cables also causes the UEM to act funny. So I wanted to see where that UEM is located to see if I had yanked a cable out somehow. So I google what the UEM looks like and google shows pictures of the rear view mirror. Turns out here's a whole electronic module crammed inside that mirror and it's responsible for a bunch of stuff. So things start making sense just a little more. if there's an electronic module that's somehow tied to my particular vehicle then simply replacing the mirror won't help. I'll have to find a way around this. But just to make sure I'm not crazy I quickly connected my old mirror and everything started working again, thankfully.

Next step was to tear this thing down and to see what's really inside. Sometimes there's a memory chip that can be removed and swapped to another module to basically transfer its memory there. Opening the mirror was a lot easier than expected as it was only held by plastic clips around the perimeter of the enclosure. And upon opening the mirror I saw what I was really dealing with.

The mirror is choc full of electronics. I mean look at that huge chip with a bunch of pins going out. Also there were a bunch of 8-pin chips, and any one of them could be a memory chip. Unfortunately though, none of them were. Funnily enough actually there was a single 555 timer in there, for whatever reason. This means that I'll have to swap the boards from one module to the other. Which is easier said than done, because the board is stuck on the glass mirror with double sided tape and I knew from experience that this tends to be a deadly combo if you try to pull something off it. In this case pulling too hard might snap the board in half and we definitely don't want that.

The easy answer to this was to add some heat. The glue on tapes and stickers tends to loosen up at around 80C, so some heat makes it a lot easier to remove. The heat has to be applied carefully, because we don't want to cook the board and whatever is on it and we don't want to damage the mirror element as we will need to remove it from the good replacement mirror. By taking the good board from the original mirror we can pair it with the good mirror element from the replacement and have a working rear view mirror. 

The board was patiently heated through and pulled off the tape, making sure to not bend it too much in the process as this could damage it. There's a sort of turning point in the whole process where you keep heating the board evenly and applying pressure until the glue suddenly loosens up and releases the board. The board is also connected to the glass element through two wires and these are simply soldered on. It is best to desolder them from the board before pulling it off. If done right the tape will simply unglue from the board and the tape can still be used to stick the replacement board on the mirror element. Which is exactly what I did. After sticking the mirror on I resoldered the two wires and reassembled the mirror back together. 

Next step was to finally install the mirror and to see if all this hard work pays off. And much to my relief it did. My keyfob finally works and the mirror no longer looks like it's filled with ferrofluid. Also shining light into the sensor on the mirror makes it darken up, which means the replacement mirror element works also.

Never would I have expected there to be an entire RF module and light control module with CAN communication inside a rear view mirror but Volvo delivers I guess. Regardless, I declare victory in this battle, but the outcome of the war remains yet to be seen. Until next time, where I find out that replacing my rusty exhaust pipes somehow makes my power seats stop working or something along those lines. 

That's it for now and thanks for visiting my blog.