Caravan Fog lights not turning on

[rikernumber1]

Hi All,

I tow a caravan with my 2011 XC60; it has the proper Volvo single electrics trailer module, and it all works as it should do, except for the fog light on the caravan.

I have extensively tested all the wiring and lights on the 'van, and all the way back to the TRM itself. There is no wiring fault, and I can get the fog lights to come on on the 'van if I connect a 12v supply directly to the pins on the caravan plug. There is nothing at all coming through on the car side, and there is continuity between the TRM and the socket.

I have connected up VIDA and the problem looks to be either a software configuration problem, or a hardware problem with the TRM. The attached screenshot shows that the vehicle is correctly identifying the fact that a trailer is connected - and when you press the fog light button the one on the car stays off; if you disconnect the caravan it comes on (expected behaviour).

To summarise:

1. The car is correctly detecting when the caravan is connected
2. The car is correctly not turning on the car fog light when the button is pressed
3. The car is incorrectly not turning the trailer fog light on.

In short - with the caravan connected I get no fog lights at all, and VIDA confirms they are switch off.

I can't see anywhere in VIDA to change the configuration. The tabs where I'd expect to make a change in the TRM config are all greyed out

My questions are:

1. Is this a config setting in VIDA I should be able to change, and if so, where? I just can't see it.
2. Is it possible in VIDA to at least change the behaviour to turn off the car fog light when the trailer is connected? If the car fog light remains on, then I can easily wire in a relay to turn on the caravan fog light.
3. Does this sound like a dealer job?

It seems a bit of a pain (and expensive) to have to get the dealer to sort this out - and if it turns out the TRM is faulty then that will be an expensive way to fix the fog light issue - which I believe is now an MoT failure, because they test the trailer socket if fitted.

Any advice welcome - TIA

[rikernumber1]

Update on this - I have been quoted £102 + VAT just for a diagnostic by the dealer. Considering I can buy a relay that does exactly the same job as the TRM for under £25 then I think I will be going that route to sort the caravan fog light out.

This is where I get really grumpy about modern cars and their overly complex electronics! It's a fog light FFS! It shouldn't be that expensive to just diagnose! I've already done the hard work of checking the wiring!

[Wagon Sailor]

Why would something like this need software in the first place? Surely the socket needs only to be wired up in parallel with feed to the car's own lights? (Or are the relays too lightweight for a job like that?)

[Whyman]

Originally Posted by Wagon Sailor

Why would something like this need software in the first place? Surely the socket needs only to be wired up in parallel with feed to the car's own lights? (Or are the relays too lightweight for a job like that?)

The software up date allows the vehicle to know a trailer is attached and the light checking system will also check the trailer lights and the ESC is adapted to allow for the trailer or caravan and save you from a potential snaking situation before you ev3n knew you had one.

[Wagon Sailor]

Originally Posted by Whyman

The software up date allows the vehicle to know a trailer is attached and the light checking system will also check the trailer lights and the ESC is adapted to allow for the trailer or caravan and save you from a potential snaking situation before you ev3n knew you had one.

Thanks.
(Not that I see why they should be part of the same system.)

[Richard M Knight]

When towing most car fog lights are turned off so you don't get the reflected glare from the trailer in your mirrors. I'm sure this is part of the software upgrade.

[rikernumber1]

Originally Posted by Richard M Knight

When towing most car fog lights are turned off so you don't get the reflected glare from the trailer in your mirrors. I'm sure this is part of the software upgrade.

I agree that's a useful feature. However, it's only useful if, in addition to switching the car fog off, it actually turns the caravan fog on! My understanding is that it is now an MoT failure if your towing electrics do not work correctly.

In terms of stability control, my 'van has that anyway, totally independent of the car. I also pay attention to how it's loaded and the nose weight; more importantly I remember I am towing a large 1.5 tonne trailer and drive accordingly! I am all for safety devices but it's more important to be sensible; I stick to just under 60 on the motorway and I have delayed or cancelled journeys if the weather is too windy.

Not been able to use it this year though 🙁

Thanks for the replies/comments

[SwissXC90]

Originally Posted by Wagon Sailor

Why would something like this need software in the first place?

Because legislative requirements vary from market to market, and it is thus much cheaper for the manufacturer to make one set of hardware for the entire word (where possible), and apply the market-specific changes by software.