Intermittent (now permanent) warning lights + parasitic drain + phantom lights — T6.1 Caravelle

[James A]

Hi all, long time lurker, first post — hoping the collective wisdom here can help before I hand it over to a VW specialist and spend a fortune on diagnostic hours.

The van: 2021 T6.1 Caravelle LWB SE (25k miles)

The problem: What started as an intermittent cascade of warning lights (ABS, power steering, TPMS — see photo) has become pretty much permanent. Alongside this I've got what appears to be a significant parasitic drain — voltage sitting around 12v after just one day of no use, and a brand new battery (fitted and coded at Halfords yesterday) drained down to 7.6v overnight, setting the alarm off at 5am. For reference, charging voltage while running is a healthy 14.6–14.9v so the alternator seems fine.

It's getting progressively worse, and I've now got some strange phantom electrical behaviour:

• THQ aftermarket front DRL headlights staying on after ignition off and van locked — I've unplugged these for now to stop them hammering the battery
• Rear sidelights occasionally activating on their own with the van parked, locked, no key anywhere near it
• Rear high level brake light flickering intermittently under the same conditions

I've seen wheel speed sensors mentioned as a cause of the warning light cascade, which makes sense, but I'm struggling to see how that would explain the drain and phantom lighting behaviour. Feels like there might be more than one thing going on, or one underlying cause I'm not seeing.

Couple of bonus questions while I'm here:

Coming from the battery I have two additional positive cables — terminals 3 and 4 — and I'm not sure what they feed. I also have a rear auxiliary heater, and a heavy gauge positive cable appearing under the passenger seat which I'm hoping is the factory leisure battery preparation. If anyone can confirm that's what it is, I'm planning to use it to connect an EcoFlow via an alternator charger.

Any pointers before this goes to a specialist would be massively appreciated. Happy to pull fuses, run multimeter checks or anything else that might help narrow it down.

Thanks in advance
James

 

[CAB]

That last picture of the battery.

The little square thing on the left is the shunt, it tells the vehicle how much charge has been used.

The white wires attached to the negative post are bypassing the shunt, so the battery is being used without the van realising.

All negative feeds should go through the shunt.

 

[airhoguk]

Do you have a code reader? Also you have an additional wiring setup on your battery post the three reds and an orange, what are they for?

 

[FWhite]

Do you have a code reader? Also you have an additional wiring setup on your battery post the three reds and an orange, what are they for?

And, more to it, the white wires coming out directly from the battery's negative pole. That is no OEM design, and potentially troubleful since it bypasses the shunt resistor that the ECU uses to determine DC current flow in any condition.
BTW the thick red wires on the 3 and 4 positive terminals are standard on a T6.1.

 

[Dellmassive]

Trailer Neg cables need moving off the battery to chassis.... (As above)

 

[Howzat]

Get all non OEM loads diso'd from the SB. Those white earths and the red/orange wires to the pos to start with.
Any piggy back fuses? Remove them and add back the correct fuse.
Get the OEM lights back in.
No point taking it to an auto electrician before doing all this. Just too many variables.

 

[James A]

Thanks for all the replies... super useful info!!

Pic attached of those white earths and red/orange wires... they all route in to a 'Trailer Module' as pointed out by Dellmassive... presuming this was part of my aftermarket towbar install. Install was a few years ago, last used the towbar over a year ago. Is there a chance this set up is draining the battery?

Charged battery up to 11.8v this morning (now back on charge to get back up to full charge) enough to start van... and guess what... all warning lights cleared . I'm sure they'll come back at some point.

Carista code reader arriving by end of today via Amazon... hopefully this may help identify the cause?

Thanks again
James

 

[Howzat]

A fault with the trailer module would be my no1 suspect seeing as they usually interface with the OEM lighting circuit which you're seeing issues with.
Get it disconnected at the battery and cross your fingers that's the issue. Good luck.

 

[James A]

And, more to it, the white wires coming out directly from the battery's negative pole. That is no OEM design, and potentially troubleful since it bypasses the shunt resistor that the ECU uses to determine DC current flow in any condition.
BTW the thick red wires on the 3 and 4 positive terminals are standard on a T6.1.

Any ideas where 3 & 4 go or what they do?

 

[FWhite]

Any ideas where 3 & 4 go or what they do?

No idea OTOH. Possibly to a bunch of fuse holders to supply everything. I have the same on mine that is untouched and I have seen them on other T6.1s.

You can download the pertinent schematics from the download section of the Forum if you really want to know. Assuming they are there, because the T6.1, especially the last variants, is still less covered.
Edit: I forgot to say that you must become VIP member (for a very small fee) in order to be able to download from that section.

 

[mondray]

A fault with the trailer module would be my no1 suspect seeing as they usually interface with the OEM lighting circuit which you're seeing issues with.
Get it disconnected at the battery and cross your fingers that's the issue. Good luck.

Like Howzat said aftermarket trailer wiring would be the first port of call. I’d be looking in the trailer socket for water or corrosion straight away.

 

[James A]

So connected the Carista code reader... had about 50 fault codes. Reset them all, but the one persistent faulty that will not clear is B200049 (see screenshot, looks like it's been an issue for a while). Does anyone have any knowledge on this error code?

I did remove the towbar electrics, however this just through up a load more fault codes, so thought wise to put back on in case I had also removed something else important without knowing.

Funnily enough, after putting back the towbar electrics, the battery voltage at idle is between 12.3-8v, whereas previously it was 13.8-14.8v. Not sure if this is because I have had the battery charging all day, but seems low whilst idling?

I will also check the towbar socket tomorrow am for signs of water / corrosion.

Again thanks for all the help here!

James

 

[James A]

Ok so update to anyone that is interested!

Left van overnight with towbar electrics disconnected... no battery drain

Checked the towbar electrics socket next to the tow ball... no signs of water, dirt, corrosion etc

Assuming the issue lay in the towbar TM005 electrics module, however all status lights look correct.

Took the van for a quick drive with my new Carista toy... all warning lights reappeared after about 100 metres... live data shows the front right wheel sensor is an issue as reading stayed at 0mph.

So... looks like wheel sensor could be the culprit, maybe also an issue with the towbar electrics module (wiring obviously need correcting as pointed out earlier in thread).

Question to the experts... could the wheel sensor be the root cause of all my issues with battery power drain etc, and also all the warning lights??

Thanks again in advance... this advice is much appreciated!

James

 

[Howzat]

... could the wheel sensor be the root cause of all my issues with battery power drain etc, and also all the warning lights??

Doubt it would cause issues when stationary but who knows and it needs fixing anyway if just to rule it out.
So I guess you're keeping the trailer module connected tonight so will be interesting to see if the drain returns?

 

[James A]

Hi all... quick update / close out this thread...

- Wheel sensor changed at the weekend, so far so good all warning lights clear and ABS / power steering etc all back to normal.

- Battery no longer draining. Not sure I have actually fixed this, maybe something has been reset, but will continue to monitor.

- Still 2x fault codes showing... will need to book in to VW at some point to have these looked at.

Again... many thanks for all the help on here, and enabling me to fix this myself with your guidance!

Regards
James