Finding short in LIN any advice
 

VIDA suggests I have a short in the LIN that has taken out the SWM I have looked around the SWM and the CEM and can not see anything obviously amiss.

Can anyone suggest how I might narrow down this search....

Easy

Get the wiring diagram for your model Volvo.
if the exact MY is not available, a year before or after doesn't matter. As long as the diagram is pre-facelift or post-facelift to match your car.

Look at the LIN bus wiring from the SWM
See what connectors it goes to
Measure resistance of LIN bus to ground with everything connected.
If VIDA is correct, it will be 0 ohms to ground (of something close to 0)
Then start disconnecting the connectors until you have isolated the fault

Example of MY2009 XC90:
The CEM connects directly to the SWM via LIN
The SWM connects to the Clockspring via LIN
The Clockspring connects to the Left buttons and the Right buttons via LIN

In electronics repair there is a saying: "if it moves, it breaks"
Thus suspect #1 is always the Clockspring.

Unplug the Clockspring from the SWM and see if the short disappears
If so, plug it back in, and then unplug the buttons in the steering wheel and see if the short disappears
If so, the Clockspring is the culprit

thanks, very logical... try tomorrow...

for this to work should it be work key out? ... battery disconnected?

i would doubt youve lost lin signal at swm

what is your fault whats not working...... lin signal should be 7- 9 volts

please update with faults

You can measure voltage with key on. As volvo_for_ever said, an active LIN bus sits around 7 to 9V DC when measured with a normal multimeter

If shorted you would see something around 0VDC

Tip:
The SWM is active from the moment you press a remote button to unlock the vehicle. And stays active continuously until the vehicle goes into sleep mode around 30s after closing and locking the vehicle, provided no buttons are pressed or functions activated


NOTE
Unplugging anything going to the steering wheel WILL cause an airbag fault to trigger when the steering wheel airbag is no longer detected.

It is not easy or visible to tell when the vehicle is properly asleep - and during any time it has woken up it monitors airbag systems.

So either prepare yourself with VIDA, or do all diagnoses with the vehicle battery disconnected and using an ohmmeter.
Observe battery disconnect precautions:
Remove key, close all doors, open tailgate, wait 10min tailgate light goes off by itself
The the car is asleep and you can disconnect the battery safely.
Always remove negative cable (black).

When reconnecting, the Volvo advice is to have key in PosI, and NO person in any seats (to ensure no airbags will trigger, as they only trigger when the seat is occupied), then attach battery promptly.

So removed airbag and unplugged steering wheel controls from clocklspring, problem solved,

unplugged cruise control and plugged back in controls, problem remained solved.

Took board out of cruise control, no signs of stuck switch or burnt component or even corrosion but undoubtedly this is the problem. replaced everything with bunch of tissue in place of faulty board and all is good in Volvoworld for now..

Thanks again to SwissXC90.

Always a delight to hear that my advice led to a prompt and successful repair!

You can pickup replacement cruise control buttons on eBay cheaply.
(unless you want to start diagnosing where the short is on the cruise control button board....)

Ill pick one up here on adverts.ie

This country is full of xc90s being taken apart because of high road tax €1038 per year and high if not impossible insurance and really silly dealer prices for repairs...