We own a Volvo V70 wagon (2002 model) and we face strange electrical behavior.

For example
-when we drive suddenly the cockpit light turns on and we can't turn them of by using the switches at the roof.
We only can activate the switch to work properly again by just removing a fuse (it is number 28).
-when it is getting warm outside suddenly our remote for opening the door locks does not work anymore, we can only open the door lock with the key.
We can only bring to work properly by removing shortly the fuse (it's number 28 (10 Amp), in the box close to the drivers door (roof lamps/courtesy lights UEM, garagedoor, etc).
However this is also happening when we have our heater on for a while, also then the remote controls stops to work properly and we need to "reset" it by just disconnecting fuse 28.


Anyone have a good suggestion here to solve this?

Thx

Alltwin

 

Sounds like a bad UEM or bad siren shutting down the UEM.
The UEM controls all the functions you are having troubles with.

 

Hi,

Would it be easy to repair the UEM?

Or in otherwords what kind of cost should I expect to repair?

Were is this UEM located, under the hood, behind the dahsboard cover?

Thanks


Alltwin

 

The UEM is the rear view mirror.

I think total it is like $400.00 to $500.00 to get it replaced. It needs software from the Dealer.

 

Hi thanks for the reply

I would have never guessed it would be in the mirror.

Would it be easy to open the mirror and check for open solder joints (intermittant contacts?) on the PCB?

Would you have other suggestions?

Sincerely

Alltwin

 

Sorry have never opened one up and checked.
You can try you cannot even do used either. The software will not load to make it work.

 

Here's a link I kept because I thought the person was very resourceful repairing his auto-dimming mirror. Step-by-step procedure with pictures that you may find helpful if you really want to take apart your rear view mirror (UEM).

Like Tech said, the alarm siren module (passenger side front wheel well) can cause problems with the UEM. There is low speed serial data interface between the alarm module and UEM and if the alarm siren circuit board is fried it can affect the UEM (and sun roof). Does your alarm siren work okay?

http://www.matthewsvolvosite.com/for...ic.php?t=16275

 

Hi there,

Thanks for this additional info.

Answering your question: No I have huge problem with my alarm as well.

It just goes of when ever it likes, even on a parking lot when then all the people are watching.

So I had to unplug the fuse, and now I got the the message something like "service required alarm"

So it's a really a mess.

Sincerely

Alltwin

 

The good news in all this may be only having to replace the alarm siren, which is much cheaper (I believe ~$175) then the UEM. Replacing the alarm siren may fix the UEM.

 

Hi There

That would be great news!!!

Would there be a method to check if the problem is really due to the siren?

Are we really talking about the anti theft siren or are we talking about the claxon, so the one underneath the hood, correct?

Suppose if we have proven that the siren is the problem, I require to replace the siren under the hood or is there a siren module or something else I need to replace?

Thanks already on forehand.

Sincerely

Alltwin

 

From what I've read you can unplug the siren module and you'll get a service message but what I am thinking is you could monitor your UEM while the siren module is unplugged for a while to see if your UEM problems clear up. Removing the fuse to the siren module may be the first option to try to see if the UEM issues clear up but I am thinking unplugging it will eliminate any possibility of the siren from affecting the UEM.

This is speculation on my part but I believe what happens with the siren module is the circuit board develops a problem (I've seen some pictures of fried siren circuit boards) or the NiMh battery goes bad and this could result in the serial interface line (1 wire) between the UEM and siren being pulled to a undesirable voltage level. The single wire serial interface is connected between the siren module, the UEM and also the sun roof module. If the line is pulled to a weird voltage level then it will affect the UEM (and sun roof). Unplugging the siren module would eliminate the module from affecting the interface to the UEM.
The siren module is located in the passenger side wheel well and is relatively easy to access. You have to drill out 4 or 5 rivets in the wheel well liner and remove the metal plate to pull back the liner.
I believe you can unplug the siren module without removing the one tamper proof bolt holding the module in place. If you do have take out the module you'll have to deal with the tamper proof bolt. I used a dremel tool to grind a slot in the bolt head and used a flathead screwdriver to remove the bolt. Sounds like you may need to replace your siren anyway. The siren has a rechargeable NiMh battery in it that goes bad and the module is a sealed plastic unit that discourages replacement of just the battery.
From all the problems I've read about the siren module I would suspect and eliminate it as the problem first before you condemn your UEM.

 

The siren is mounted behind the R/F inner fender liner.

If you had the codes pulled it would tell you if the siren is bad.

 

It didn't quite work out that way for me. My Alarm Siren did fail, and the text message did tell me it needed servicing, but it did let me open the roof only to not work after I shut the car off and later need to close the roof.

I tried clearing the error with all the tricks from removing fuses to disconnecting the battery but I could not get the roof to shut. I pulled the overhead courtesy assembly and the UEM mirror assy, and started probing the wire harnesses at the connector with +12V. That apparently reset something so I could operate the roof again.

The 5a fuse for the alarm and the sunroof fuse is now out for good, or until I find a new Alarm Siren for cheap...

I infuriates me how over-engineered these cars are, while offering no backup systems or work arounds/resets for the software.