Nothing on the roof works 01 XC70

[jpgurley]

I recently purchased this 2001 XC70 and nothing above the glass works. Power moonroof, interior lights, vanity lights, rear hatch light, etc. all are dead. The lights below the dash come on with the doors open but that's it.
All fuses are good. I suspect a loss of ground somewhere or some module failure. Where would I find a common ground and/or the "brain" that controls all of those? If it is the module, can I get one from the junkyard and plug it in or does it need to be programmed by the dealer?
Any advice on how to fault trace would be appreciated.
Thanks in advance for your help.
Jon

[SuperHerman]

I would start by looking at your Siren Module. These are known to go bad as the batteries leak and ruin the circuit board. This circuit is tied into a number (if not all) the items you mentioned. Sometimes you can cut it open (many write ups) and clean it up and repair it - then fashion a new battery substitute. Otherwise you can buy a new module and it should be plug and play.

It is located in the pass side wheel well area. You may be able to see it by removing the headlight, but most pull the wheel well liner.

Look at your fuse panel and look for the siren module fuse. See what happens if anything if you remove the fuse. Although you may have another issue, that is where I would start.

[precopster]

The "brain" or central controller is known as a CEM and is located to the driver's door side of the steering column . You need to remove the kick panel with 2 x T25 screws and look up. You'll spot a white metal bracket that can release the CEM partially and allow it to drop for more disassembly.

With so many modules affected it's very likely rhe CEM is faulty. Officially speaking Volvo dealers will not get involved in replacing the CEM with a used one. They will only replace with a new one for ridiculous money.

The rear vision mirror known as UEM controls power roof, roof console lights. The REM is located behind one of the rear side hatch panels and controls the tailgate light. The REM has multiple fuses you can check.

Unofficially speaking you have Henry and Sergey and XeModex in Canada cloning used CEMs all day long.

An initial reading of the car's diagnostic port with Vida and a Dice tool would likely reveal some miscommunication between modules.

By all means check all fuses and replace them if you find any that are not intacr.

[jpgurley]

Ok guys, great advice. I hope to visit a self serve junkyard with great prices soon. If I can score an alarm unit, a interior light/ sunroof assembly (UEM) and the (CEM) module behind the left kick panel, how many of them will be plug and play?
I get the impression that any used CEM can be made compatable (like an unlocked phone?) So my last question is can I use a UEM or CEM from S80/S60/S70 etc?

I'm an old school mechanic (from the 70'S) and have had great success fixing these cars with bent valves, but this networking stuff confuses me! How can a three wire alarm unit effect so many things? Boggles my mind.

Hope I can hunt up some fixes at the local pick-a-part.

[SuperHerman]

For modules usually one can get by with a like for like year and model and engine swap.

Volvo uses many of the same modules in various vehicles but they are loaded with different software. Sometimes cross platforms the software may be the same, sometimes not. That is why like for like is best approach.

On some modules it does not work so you have to do some research on the specific module you are looking at.

For the siren module I believe it is plug and play across all cars as when I bought the new unit, applicable to various models, I just plugged it in with now programming and it worked.

[jpgurley]

Half my problems solved! Well, sort of.
I found that the multi-pinned green plug on the back of the mirror was unplugged! Upon getting it seated all the lights work normally. My biggest question now is who and why was it unplugged? I have no history from previous owner on this car. Perhaps someone unplugged it when replacing the windshield. But why? I will keep an eye on it to see if there is any other malfunction.
So. . . I am certain that the siren module will correct the moonroof problem but I can live without both those functions for now.. I will get around to it later and post here to confirm your diagnosis to be correct.
In the mean time thanks for putting me on the right track. You guys are so helpful for DIY's and old school mechanics like me.
Blessings,
JPGurley

[precopster]

CEM has unique code for keys and is paired to ECM key latch. CEM also has the car configuration, mileage and options.

CEM can be cloned by guys here on forum by either sending it to them or cloning it over the internet with a Dice reader and laptop.

UEM is paired to the remote control board of a key fob so if you get a new UEM try to get the matching remote.

The transponder (small glass capsule) in the key fob is paired to the CEM so the car can start.

Rear body modules (REM) is usually the easiest to pair due to few changes in software, but best to stick to same vehicle type (sedan or wagon) and same model year

[jpgurley]

Problems solved!
As I mentioned in my post on October 21st the mirror wire connectors were unplugged so that fixed the interior lights etc.
However the Moonroof (Sunroof) still did not work. Now that the rains have stopped here in NC I was planning on going to the self-serve junkyard today. However I found a post from another link on this website that helped me realize that there is a procedure to disconnecting and reconnecting the battery on P2 Volvos!
I never knew that!
After following the procedure the sunroof works.
I am a happy camper.
I do not have the Alarm Service required notice on now, it still works as designed but no sound. I can live with that.
Here is the link to the procedure that every P2 DIY driver should know. I would have never tried hooking up a battery on a car with the ignition on.

https://howardsvolvos.webs.com/miscissues.htm#207347288

Thanks for your help.

[precopster]

Thanks for closing off the thread. The battery procedure is well known here but good to have it once again show us it works for the sunroof