Caravan/towing electrics issue.

[Magicdrshoon]

I have just replaced the 13 pin socket on the back of my 2013 MK2. 

 

Turning the lights on in turn, I used a multimeter to test the individual pins to make sure they are all wired correctly, including the feeds and resistance checks on the grounds.

 

When I plugged the caravan in to test on that, a bunch of the lights weren't working (none of the lights on the left side and neither break lights) and the car is complaining about several bulbs going. Plus, for the first time it's gone in to towing mode where when you select reverse it shows a picture of a trailer attached and it deactivates the reversing sensors - and it's stuck in that mode whether the caravan is connected of not (as are the warning lights for blown bulbs). I've cleared the faults on the canbus but it still thinks the bulbs have gone.

 

The car's bulbs haven't gone and they work perfectly, but the left indicator clicks inside the car at double time, but flashes normally on the exterior (both front and back).

 

I tested the voltages again on the connector, only this time they are not showing where they should be. Not in the wrong place, just not where they should be - the left indicator has no voltage switching on and off on that pin.

 

We're supposed to be off to France in it in the next few days so need to get this sorted ASAP!

 

I'm beginning to think either an issue with my dodgy wiring (or I've disturbed someone else's), or one of the control units has coincidentally gone faulty (it's been occasionally flashing "Check trailer bracket" since I got the car many years ago).

 

Any insights or ideas would be greatly appreciated.

[gumdrop]

Could you say which 2013 mk2 model you have and the make, model,  of caravan you have, please this will possibly get you help quicker.

[Magicdrshoon]

I plugged a different car into the caravan which has confirmed the caravan is working fine.

 

I do have to use a 12n/s to 13 pin adapter as the caravan has the old 2 connector wiring.

 

The car is an L&K edition 2.0 diesel with DSG.

[Magicdrshoon]

I've unplugged the trailer module (52502504C) and the bypass module, cleared all the faults, then reconnected the trailer module and at least the car is now behaving normally when the caravan isn't connected.

 

As soon as I connect the bypass relay (specifically the +12V)  the dash shows bulb errors and starts misbehaving again.

 

With both units disconnected there's 0V on this wire that's supposed to be the +12V feed for the bypass relay, and when I plug the trailer module in it goes up to +4V.

 

The bypass relay seems to have been wired incorrectly before too, with the fridge power going to 2 on the relay.

 

I've also spotted that I have a 15A fuse blown which may or may not be related - for the rear window wiper (which the hatch doesn't have!).

 

 

[chimaera]

Sounds like an aftermarket wiring kit. Can you post make/model for the controller and bypass relay?

 

Get the wiring diagram for both controllers, and the car, and confirm that all wiring is correct to start with. Also check that your 13-pin socket is wired correctly.

 

Figure out where the three power supplies for the caravan are being fed from too.

 

Some towing controllers won't activate unless a trailer is connected, so probing individual pins may not produce the results you expect.

Edited 12 August, 2023 by chimaera

[Magicdrshoon]

These are the modules.

 

I would love to have a wiring diagram for the car - any idea where to get one?

 

The connector that plugs into the trailer module seems to be direct from the main loom (I.e. Not aftermarket). Also, the reversing sensors won't work without this plugged in.

 

The bypass relay seems pretty standard. Note: this photo shows the wiring before I disconnected it. I added the black tape to the left-hand orange wire so I could distinguish it from the other one!

[chimaera]

You can purchase the official Skoda service manuals from https://erwin.skoda-auto.cz/erwin/showHome.do including wiring diagrams. An hour's subscription is usually enough to get everything. You'll need your VIN handy to register.

 

Can you show a picture of the connectors going to that module? Let's assume nothing about what's there since you've already spotted problems with the original installation. It would be really strange for someone to go to the effort of fitting the OEM wiring harness and not spend the little bit extra to fit the controller to go with it. Unless you strip down the boot liner panels and verify that the wiring is OEM it's safer to assume it's not and proceed accordingly.

 

The reverse sensors should function normally with the controller unplugged, so this is a red flag. The correct way to handle parking sensors is send a signal over CANBUS to the parking sensor controller to disable the rear ones while a trailer is connected, and instruct the screen to display the trailer icon instead of the rear sensor position. Unplugging the controller should have no effect on the rest of the CANBUS network.

 

For curiosity's sake, have you connected the caravan with just the lighting controller connected i.e. leave the bypass relay disconnected. This would help narrow things down - if the lights work normally without the bypass relay then we can focus our attention there.

 

Proceed with care all the way along here - spurious voltages flying around the car can cause expensive damage to control modules. Check everything carefully.

[chimaera]

Ok, having done a little digging on this controller, it's not using the OEM harness, it comes with its own which is fitted in a similar manner to the OEM one, connecting to multiple fuses at the fuse panel (should be 43, 44, 45, and possible 8 & 9), and hooking into the CANBUS at the BCM. It looks like it may also have the additional power supplies for the caravan included internally like the OEM controller does (if fuses 43/44/45 are fitted it almost certainly does since these positions are reserved for this function).

 

That bypass relay seems to be a pretty basic dumb one and shouldn't be connected to the towing controller at all. If the controller has this functionality built in, then having this relay fitted as well would definitely mess things up.

 

Provided the correct power and CANBUS connections were made at the fuse panel/BCM it should just work, so as I suggested above I'd disconnect the bypass relay and see if the lighting functions are ok. It would be worth checking pins 9 & 10 on the towing socket too to see if they are showing 12 V - if they are then you can bin that bypass relay.

[Magicdrshoon]

Thanks for your advice @chimaera! and for spending the time to look into this and reply. Very much appreciated!

 

It turned out to be that bloody fuse! All I can think of is that as someone had wired the bypass relay incorrectly they compensated by also wiring the 13 pin connector wrong to make it work, so when I wired it correctly it blew the fuse (either that or I accidentally tapped the +12v to ground somehow - maybe more likely!).

 

I did try leaving the bypass relay disconnected and connect just the trailer connector (black one) to the caravan but it still didn't work right.

 

There are no fuses in 43, 44 & 45. I noticed they were labelled as for the trailer and was surprised there wasn't any there.

 

I can't remember what number it was (39 maybe?) but it was the fuse for the rear wiper, which of course it doesn't have.

 

I have another thread I started when I first got the car about it randomly saying "Check Trailer Bracket" - perhaps this was the problem all along! And it's never shown that a trailer is connected when selecting reverse (I don't know if that bit works yet - will find out on Tuesday!).

 

Thanks again!