Ongoing problems with Volvo XC70 and caravan brake lights
Ian
new Volvo XC70 and the brake lights on his Swift Challenger caravan. The
towbar was fitted by a reputable towbar company to a brand new Volvo XC70.
The caravan had worked fine with his old car (Nissan X-Trail) and also my
car (Honda FR-V). When attaching the caravan to the Volvo everything seemed
OK for the outward journey but when hitching up on the way back he could not
get any brake lights on the caravan to work (all car lights and also all
other lights on the van working OK). When he got home I checked the supply
on the 12N plug at the back of the car and got voltage when brakes applied
with a multimeter. I also tried the caravan with my car and all was OK. His
Volvo was checked by a Volvo dealer while in for a service and they used a
trailer board and it was all fine. To appease him (my mother-in-law will
probably be reading this!) I replaced the 12N plug on the van in case it was
a problem with the connection......same result, Volvo no brake light, Honda
no problems. He has now contacted the caravan supplier and their comment was
"...oh no not another Volvo with problems..". Anyone else had any idea what
could be causing this problem? Someone here suggested making sure the
ignition was fully off while hitching up. Tried that and made no difference!
Please ..... anyone?
regards,
Ian
Dougal
What's different?
The only thing is the caravan vs the Volvo dealer's trailer board
leading to the conclusion that they are not electrically equivalent.
The caravan will have 2 x 21W (or whatever is used these days) bulbs in
parallel. Did the dealer's trailer board apply an equivalent 42W load or
is it just registering the presence of voltage?
The difference from the car's point of view could be a 42W + a bit load
with the trailer board or (42+42)W watts with the caravan which it may
not like.
I'd be tempted to see what happens with a trailer board (two bulbs in
parallel connected to the relevant pins will do) with a known 42W brake
light load. If that fails it's back to the Volvo dealer to ask what
load their trailer board applies and what is the effect of adding an
additional 42W brake light load to the car circuit.
It does, however, not explain the apparent working lights on the initial
journey. How certain are you that this is fact?
Ian
news:CZCdnZPipZ1SZOfW...@eclipse.net.uk...
Thanks for the info. Regarding the initial working of the lights, I am 100%
certain as I had to phone my mother in laws mobile when they set out as they
had forgotten something and I could see them about 200 yards away coming to
a stop when I called and would definetely have noticed if the brake lights
didn;t come on. Also my father in law is quite a stickler for checking
everything before setting out.
regards,
Ian
Dougal
What I'm proposing is either that the Volvo has a fault (possibly a
failure to install the trailer socket correctly and/or program the car
to take it into account) or that it is clever enough to recognise an
over-current situation and is reacting to protect itself.
This car is not conventionally wired in the old way but is CANbus with
computers spread around the car. This type of system lends itself to
being able to have 'protection' built in.
There is a circuit for the 2005 models on the web if you want to try to
understand the it, but if you're not up to the symbols it's like Greek!
http://www.wiringdiagrams21.com/2008/10/02/2005-volvo-v70r-xc70-xc90-car-wiring-diagram
There are some Volvo installation documents at the end of the page with
this link
http://www.volvoclub.org.uk/towbar_electrics.shtml
I'm assuming that the towbar installer also installed the trailer
socket. Does he understand the Volvo circuitry?
Paul - xxx
This may be a red herring but we recently had an isue with our caravan
only when being towed by my Disco .. trailer worked fine, caravan
lights all worked fine, but the trailer 'tell-tale' light on the dash
always went out when I applied the brakes, and stayed out. When it did
this all indicators would still work and all brake lights on Disco and
caravan. Eventually traced to the offside brake light bulb .. filament
was broken but hadn't sprung apart, so worked intermittently ... I
suspect the Disco sensed when it wasn't working and stopped the
tell-tale .. new bulb and all was well.
Perhaps a new set of brake bulbs might help, whether they look broken
or not?
--
Paul - xxx
'96/'97 Landrover Discovery 300 Tdi
Dyna Tech Cro-Mo comp
Woody
That's a very good point. My last Co car (Astra estate that also
uses CANbus) had a towbar fitted by the supplying dealer - a
large reputable organisation that supplies huge quantities of Co
vehicles.
When I connected my 'van nothing worked. I checked the socket and
the relevant pins were dead. The supplying dealer was too far
away but as the car had been ordered on Vauxhall with towbar it
was covered by warranty so I took it to a well known outfit who
are Vauxhall main dealers. They couldn't find anything wrong,
save when I go it back a missing fuse had been inserted and the
12S static supply was now present.
Still not satisfied (obviously) I took it to my local (still big)
dealer who, after some pressure and a few calls from Vauxhall
instigated by the lease co they found the problem. The towbar
comes with a ready-made cable and plug to go into a
switching/relay panel inside the N/S/R wing. It had been plugged
in to the wrong place: fair dues there are two places that the
plug would fit and they had chosen the wrong one (I think they
said the other socket is only active when ESP has been
activated - which had not been ordered!)
One thing I did find out with that car (as it is with my new one
also) is that it detects bulbs and if one is not present it does
not attempt to switch it. Vauxhall in their infinite wisdom fit
the luggage area light on the N/S just below the tonneau cover
catches. Hence put a bit of luggage in the car and the light is
useless. I fitted a 12V flourescent in the roof - superb. Only
problem was that if I had switched the light off during the day
and opened the tailgate at night, even when I switched the lamp
on it did not light - I had to (completely) shut the tailgate and
re-open it to make the fitting light up.
Could this Volvo be suffering the same issues?
--
Woody
harrogate three at ntlworld dot com