XSeries-forum

Greetings everyone,

Does anyone have experience of renewing the SOS telematics battery below the sharksfin? For the past couple of years the car has shown the SOS failure message either when the air temperature is below about 15 Deg or the it has been standing/only done short journeys for a week. The warning has disappeared during the past couple of heatwaves which suggest the battery has just enough charge to make the system work. However,the warning is coming on each time the car is started now (it's cooler up here in NE England this week). Longish journeys or warm days make no difference. I've heard corrosion can be a problem too. However, until recently, its behaviour on warm days or after longish trips which charged the old battery makes me suspect it is giving up the ghost - so is it the first problem to solve? It's the original battery so is now is 8 1/2 years old. As ever, your thoughts please?
Graeme

There a two possibilities. There’s a Telematic Comms Box located in the left rear wheel arch, and a Telematics Control Unit mounted in the roof. Both may have emergency batteries (there are versions without) and it needs fault diagnosis to confirm which one is misbehaving

The procedures in the roof depend upon whether you have a sunroof or not. However in both cases you need to do the following preliminary work:

Remove right grab handles.
Remove the right trim panels for upper body pillar (B-pillar).
Remove the right C-pillar trim panel (C-pillar).
Remove the right C-pillar trim panel (D-pillar).
Remove the right backrest side section.

What follows depends upon whether or not you have a sunroof as there are screws and clips to be removed before you lower the right side of the headlining and rest it on the head restraints so you can get to the telematics unit.