T6.1 OEM Towing Socket behaviour

[roadtripper]

So today I have been tinkering with my towing socket and thought this might be useful info in a post for others.

My van is a MY21 T6.1 Caravelle with full towing electrics from factory. (Edited to add mine is a single battery system)

This is my experimental 13 pin plug. There are 4 grain of wheat 12v lamps connected to the 2 sidelight and 2 indicator circuits as that's the circuits used for trailer detection. Also there is a CTEK charger connector to test the battery lines.


Trailer detection

Shortly after plugging in the grain of wheat lamps flash in sequence. This happens.even if the van is locked.

I don't think that the socket has a switch for plug detection (none is shown in the wiring diagram) so it's interesting that the ECUs are still monitoring even when locked. I have not had the patience to leave the van for an hour or so to see if this goes to sleep (yet)

Further testing reveals that the trailer ECU keeps the permanent live on for quite some time after trailer detection has occured, this confused some initial conclusions.

Lamp failure detection

I thought only these 4 lighting circuits used for trailer detection would be monitored for lamp failure but I do get a warning about brake lights.

That's slightly annoying as I had a fifth grain of wheat lamp I could have used for my virtual trailer. However in retrospect I think this may be an advantage, getting a warning about a failed brake light is a useful warning the adaptor is plugged in still.

Permanent Live (pins 9/13)

When connected to these pins the CTEK lead has 12v on it's pins even with the van locked. However the virtual trailer lamps are required for the initial trailer detection to occur and pin 9 to go live initially.

This was one of my main goals as this looks like I can use this as a maintenance charger and basic 12v EHU.

Without the virtual trailer lamps eventually the trailer ECU and the permanent live will shut down, I've not measured but it would seem to be a few hours. However with the virtual trailer lamps connected it seems to stay live and has been tested to 5+ days below.

Ignition Live (pins 10/11)

When the CTEK lead is connected to these pins there is no voltage on the CTEK lead pins in any state if the virtual trailer lamps are removed.

With the virtual trailer lamps connected there is voltage when the engine is running but not if the ignition is on but engine off.

I've not studied the voltage over time in detail to see if the ECU is doing anything like leaving the feed off while the van is replacing the startup charge, or if it only enables when the smart alternator is charging. It appears to be simple logic of engine running + trailer detected = pin 10 live.

This is disappointing as I had hoped this would be "dumber" and not aware of the trailer detection, then I could intercept this circuit under the seat to use as a charging source for my power pack. I guess I still could by using a similar trick with small lamps, but there are undesirable side effects of the van thinking it has a trailer at all times.


Hopefully that's useful to some folks. The good thing is the permanent live is live even with van locked so long as a virtual trailer is detected. That allows me to easily maintenance charge and to use the charger as a basic EHU which was my main aim. It's easy to assemble the adaptor, long term I will need to seal the cable entry or fill the inside with some neutral cure silicone.

 

[Captain Quick]

Permanent Live (pins 9/13)

When connected to these pins the CTEK lead has 12v on it's pins even with the van locked and, crucially, also with the virtual trailer lamps removed.

This was one of my main goals as this looks like I can use this as a maintenance charger and basic 12v EHU.

I've yet to check if this stays live when the van has been locked for some time and maybe ECUs enter a sleep state.

@roadtripper That’s very interesting. When I tested the trailer socket on my campervan (built on a 04/23 LWB Highline 4Motion DSG 204PS Panel Van with factory-fitted tow bar) recently with the same aim as you, I detected no voltage across Pins 9 and 13 with the ignition off, locked (and not connected to EHU) 24 hours after locking, and presumably in sleep state.

 

[roadtripper]

In the week I'll double check what mine does in sleep state. I did double check Pin 9/13 after an hour or so and it still had voltage, will see what happens after a day or so.

 

[roadtripper]

OK some updates, both good and bad.

Having left the van to sit for about 3 days I found like @Captain Quick that there was no voltage, just a flickering few millivolts that might have been monitoring pulses.

So it looks like the trailer ECU does eventually sleep.

More disappointing news, when I unlocked the van and went to ignition on there was no change.

However when I reinstated my "virtual trailer" I saw the sequence of lights, got the brake light warning and Pins 9/13 went live.

So my conclusion is that you need the trailer detection to "wake up" the trailer ECU but it then stays awake for some time after locking. Not ideal but I can work with that. It would be fine for the 12v EHU use case as I could just fit the minimal 2 very low wattage grain of wheat lamps in the connector to trigger the detection, the dash warning about missing lights would remind me I had it connected.

In good news the CTEK seems happy now everything is awake. So I'm going to leave it connected and see if this state will keep the trailer ECU awake or will it shut down.

 

[Captain Quick]

That sounds promising @roadtripper. I’m looking forward to seeing the results of your test to see whether the towing ECU remains awake (with your virtual trailer connected) for long enough to charge the starter battery.

 

[roadtripper]

Well 10 hours later we are charged.

I was going to have the van out tomorrow but may take the XC70 and see how long it will stay in this state. For science

 

[Captain Quick]

Time to fire up the Amazon app I think…

 

[roadtripper]

So at the about the 36 hour mark since I locked up and still live. Taking photos mostly for the timestamps.

Of course I want to do some tinkering in the van for the Bank Holiday but also don't want to disrupt the experiment...

 

[roadtripper]

Now at the 3 day mark since locking and trailer ECU still awake and full lights on the CTEK. It hasn't dropped into the final maintenance stage yet.

Clearly enough for the 12v EHU use case, I want to keep pushing a bit longer for the maintenance use case, probably will run out of patience at the 5 day mark

 

[roadtripper]

Right tonight has to be endex as I need the van tomorrow. CTEK was still happily charging after 5 days and 9 hours.

I'll update the original post and maybe do a "How I Done It" style thread for making the connection up.

 

[Captain Quick]

Right tonight has to be endex as I need the van tomorrow. CTEK was still happily charging after 5 days and 9 hours.

I'll update the original post and maybe do a "How I Done It" style thread for making the connection up.

Nice one @roadtripper. Looks like you’ve identified a viable solution after all.

Just out of interest did you wire GOW bulbs to all of the ‘virtual trailer‘ plug pins or just the ones for the positional lights? I had thought of using LEDs with appropriate value resistors instead of GOW lamps, but wondering if this would add complexity and cause error messages.

 

[roadtripper]

Nice one @roadtripper. Looks like you’ve identified a viable solution after all.

Just out of interest did you wire GOW bulbs to all of the ‘virtual trailer‘ plug pins or just the ones for the positional lights? I had thought of using LEDs with appropriate value resistors instead of GOW lamps, but wondering if this would add complexity and cause error messages.

You want just plain GOW bulbs, not LED as they don't reliably trigger trailer detection.

Theoretically you could use a resistor but I feel more comfortable with actual lamps, plus you can see what is going on if you need to.

I've done a full how to thread now:

https://www.t6forum.com/threads/trailer-socket-12v-ehu-how-I've-done-it.45009/

 

[Captain Quick]

Cheers @roadtripper. Excellent write up. I noticed you mention that if a factory second battery is fitted then Pins 9+13 are most likely connected to the second battery on a late T6.1 model. That suggests that the vehicle starter battery will not be charged if a CTEK charger/conditioner is connected via the tow socket. It therefore looks like it won’t work for me and I’ll have to hook up to the starter battery circuit under the passenger seat after all.

 

[roadtripper]

Excellent write up. I notice however that you mention that if a factory second battery is fitted then Pins 9+13 are most likely connected to the second battery on a late T6.1 model. That suggests that the vehicle starter battery will not be charged if a CTEK charger/conditioner is connected via the tow socket. It therefore looks like it won’t work for me.

That's what I have gleaned from the forum, I don't have access to one to test!

I've not yet found it in the wiring diagrams.

 

[roadtripper]

You could fit an AMT-12 which would be useful in other situations.

 

[Captain Quick]

You could fit an AMT-12 which would be useful in other situations.

Possibly, but I‘d like to utilise the CTEK for the time being to maintain the starter battery until I can get round to installing a 200w solar panel and a Renogy DC-DC + MPPT charge controller. I’ll probably use a piggy back fuse connector under the seat with a CTEK direct connector adapter and just plug in my MXS 5.0 as and when I need to.

 

[roadtripper]

If you're a T6.1 like me then you will have the handy additional plate fuse box on top of the battery, so dead easy to fit a quick connect between that and the wing ground bolt.

Then if you get a quick connect extension that will easily fit through the closed bonnet seal to a waterproof box with charger and give you almost the same solution.

Under bonnet pics on this thread:

T6.1 under bonnet electrics

So I've been considering adding a BM2 and a CTEK connector to my single battery MY21 T6.1 Caravelle with the thought of possibly mounting the CTEK 10A charger there as a basic 12v only EHU. Lots of folks seem to use the space around the battery like this but mine doesn't seem to have the...

www.t6forum.com

 

[Captain Quick]

That’s what I’d been considering. However, my preference is to plug the CTEK MXS-5.0 battery charger into the 240v/13A socket inside my van (with the van on EHU) and fit a CTEK quick connector to the Battery Isolation Relay, Fuse Holder G Fuse 1 (under the front passenger seat). This fuse is directly fed from the lead connected to SJ2 in the plastic box on top of the starter battery in the engine compartment as shown in your Underbonnet Electrics thread.

 

[mmi]

However the virtual trailer lamps are required for the initial trailer detection to occur and pin 9 to go live initially.

I would expect the functionality can be coded similarly to T6 (below, always active).

 

[roadtripper]

I would expect the functionality can be coded similarly to T6 (below, always active).
View attachment 214075

Interesting...

I'm trying to avoid the temptation of VCDS and keep things "stock" till the end of the initial warranty but this and a couple of other things are tempting.

What I'd be most interested in is if this could be done on the switched live Pin 10, because then I have an underseat ignition switched 30amp feed...