Ring Loop MOST issue
 

I have decided it's time to sell my 2004 XC90 so took it to my local hand wash for a full valet, they did a first class job and it's never looked as new. BUT, while washing the carpets they have obviously caused some sort of problem as this morning the radio want turn on and the sat nav won't raise.

There is power getting to the radio as I got it to bring up the welcome message and then it went blank again. I can use VIDA to activate the buttons and see the state of the buttons when I press them so there is some sort of power/connectivity.

There is an ICM communicators error that comes up and reading the details it says there could be a ring loop / MOST issue. I'm not so good at this point of technical detail but it seems to me like maybe moisture or condensation has got into the fiber optic MOST cable which could be causing a communications error OR maybe one of the ring modules has been knocked.

Can anyone explain how to use VIDA to try and track down the route of the issue, it talks about pulling the ATM fuse for 30 minutes but I can't even find reference of which fuse it is.

Help!

Remove the audio amplifier under the right front seat.

The MOST bus goes via the audio amplifier

Check the amp for water ingress.

The fiber is the orange cable, ensure it is not damaged.
Make sure the amp has power (measure it)
If anything is wet, remove it and dry it thoroughly

Note that the gyro sensor is also in the same hole, I believe

Thank you SwissXC90, appart from the amp are there any other ICM related modules aroudn the floor areas where they could get wet from carpet washing?

I've read you can use an optical loop lead to bypass the amp etc if it is damaged.

Just add MOST fibre cables do not like sharp radius bends in them as it disrupts the light beam. Check the routing of the cables that were likely in the vicinity of a valeter. They may have moved accidently a fibre cable and bent it beyond its working radius.

Thanks for this also. It's dark now so I'll have a prod around after work. Maybe take the drives seat out to give full access.

Dark is perfect
On every fibre cable you should see one emitting red light (the optics are generally in the visible red spectrum)

Refer to the wiring diagram of your car:
http://www.volvowiringdiagrams.com/

If you cannot find your model year, choose the closest model, the MOST bus is the same in all the models

Removing the amp
 

Hi,
Sounds like water has got somewhere.
On my 2006 model the fibre link was wrapped together with the wiring loom for the amp making a very tight and thick cable which would be difficult to kink.

The fibre ran to the centre console, then along the drivers side of it just behind the carpet trim panel which pulls off easily, before going up towards the head unit.

Removing the amp was easy, just three 10mm bolts and lift it out, however the power lead to mine, (closest to the door) was very short making access extremely difficult. I was worried about bringing up a fault code if I removed it, but glad to say that with the keys out df the ignition it can all be disconnected and re connected with no problems.

The fibre disconnects just the same as an electrical multi-plug.

It should be easy then to test the amp power.

Photo attached, please ignore the OASI bluetooth connector, you should just have two orange fibres together.

Great, thanks for the info.

Does the seat need to come out to get at the amp or can it be moved out without taking the seat rails out?

Just slide the seat all the way back and you can just about do it.

don't forget to raise the seat
 

If you also lift it to the fully raised position there is plenty of room