Towbar Permanent live

[JohnDavo]

Does anyone else tow a caravan with a new XC40? ( 23 plate). The towbar electrics should have a permanent live for the ATC ( caravan stability system)
I have a 23 plate XC40 B4 mild hybrid. When hooked up, unless the engine is running, sometimes what is meant to be the permanent live switches off and then comes on again, each time with ATC going through its checking cycle.
I previously had a 69 plate XC40 and this did something similar in that sometimes you needed to open a door to get the ATC to come on. Dealer suggested there maybe no really permanent live anymore as the car will switch off anything when the battery is a bit low and something is draining power.
New car seems to do this more often though and I suspect its being too clever for its own good. This is not good for the caravan.
Anyone had anything similar??
Thanks
John

[Felindre]

My21 with the towing pack. Yes the 'permanent live' is switched and only comes on in my observation with the ignition (not necessarily with the engine running). But even only coming on with the engine as you suggest, stop start is disabled when towing so once it's on it's on until YOU switch off.

[JohnDavo]

Thanks for you reply. My previous 69 plate XC40 was similar to this. However, with my latest 23 plate the stop start is not disabled for towing . Also I notice with the ignition off the ATC switches on and off sometimes. I suspect its the car monitoring power consumption etc. Bit worrying with ATC attached

[Felindre]

Sounds to me like your car wasn't coded properly for towing. The 12v permanent live needs to be there for the fridge so the car should not be going into stop whilst the trailer is plugged in.

[ChrisLF]

Whilst I have and will have a tow bar I won't be towing a caravan. But out of interest, knowing that the stop/start can't be turned off manually with the mild hybrids when not towing are you saying that it is disabled when towing and the engine doesn't stop?

Edit: Just checked the manual and that indeed is the case, and as per the previous system, there are other situations when the stop/start doesn't activate. It says trailer in the manual but that may not be the case with mine being a domestic one, though good quality Ifor Williams, with less electrical connections than a caravan. Won't be a problem for me though if the stop/start does operate.

[Felindre]

Yes, even when towing my tiny trailer, whilst hooked up the stop start doesn't operate. I believe the system senses the lighting circuits to detect hook up, as my little trailer is only a 7 pin wiring connected through an adapter to the 13 pin on the car.

As mentioned the 12v is also used for the ATC anti snaking system so would need full time power as every time it receives 12v it goes through a test sequence.

Other things happen when you're hooked up, you should also find the rear fog light doesn't come on on the car (so you're not blinded by the bright light reflected off the caravan), but does on the trailer, and if you have BLIS this will be disabled. This should alert you with a message on the dashboard that it's disabled as a trailer has been detected.

[ChrisLF]

I get the "Check trailer lights?" When I hook up which I assume you get with the B4s? All clever stuff, though I still check them myself as part of my checks before pulling away.

[Felindre]

Yes the self test it does it great, it even gives you time to press OK and then walk to the back of the caravan before it starts.

[JohnDavo]

Just reread my handbook and it does say that the 12v permanent live will switch off if the system needs to conserve power for the starter battery.
So all you caravan towers, be aware!!

[Felindre]

Pretty sure that is a left over phrase from when the usual 12v battery was referred to as the 'starter battery' as they had a small motorbike style 12v battery for the accessories.

This system changed with the B's, and I can't ever imagine the 48v battery in the B's going flat as it's ONLY used for starting and gets recharged on every braking. Though some have had issues with the 12v battery going flat due to the voltage converter (the generators 48v so this is required to charge the 12v)