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Discussion Starter #1
Hi all, I have spent the afternoon removing the towbar from my t5.1 and I have created a problem...

The bulb failure/ lighting system orange fault light on the dashboard is lit.

When I indicate left or right the dashboard green indicators flash at double time...all the outside actual indicators flash at normal speed all lit and working perfectly.

When I try the hazard warning lights they work perfectly and flash at normal speed on the dash as well.

The Thule towbar all came off easily and I removed the wiring from the engine bay back to the towbar. The wiring is a nice trailer module kit made for the t5 by the looks as it had connectors for underneath the seat to connect into a wire that has connectors on it.. presumably to make fitting a kit easier.

I suspect the problem maybe caused by 2 wires that come off the towbar main loom up from the engine bay into the van up towards the behind the dash area...I just cut these as I didn't have time to investigate where they went....so these are the prime suspects !

Does anyone have any idea where these 2 wires might go, would they connect to a relay or into the indicator system somehow..?

All help, suggestions and advice appreciated before I take the whole dash apart !
 

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It's hard to know for sure, depending on exactly what type, but if it's a dedicated loom then the towbar controller will have several connections into the dash area and/or under the passenger seat. Two that should definitely go to the dash area are the CANbus connections. If you remove a dedicated setup you need to modify the van's coding accordingly.
 

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Not a Thule bar, but when I fitted tow bar and electrics to our T5.1.1 single cab tipper. The main vehicle loom had to be unplugged under the steering column and pins changed to integrate the towing loom.

So perhaps this needs reversing to resume normal play?

Rightly or wrongly nothing has been changed in the ecu settings as the trailer lights work. Only occasionally get an issue with plugging trailer in with the lights on, then you get the bulb out warning.
Will eventually get the settings done!
 

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Rightly or wrongly nothing has been changed in the ecu settings as the trailer lights work.
From memory there are a couple of things that won't work without coding changes to the control modules - firstly the ESP "trailer mode" won't be enabled when a trailer is plugged in, and also it won't automatically inhibit the van's rear fog light while you are towing.
 

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Discussion Starter #5
Thanks for the input so far I will have a better look this afternoon to see which kit was fitted and where the 2 wires I cut went..I suspect canbus from the advise given in replies above !

My t5.1 is an ex Mercedes recovery assistance van so had all the tow bar stuff done at a dealer in the north it’s 140 with dsg box and parking sensors fitted from factory so I suspect some vcds coding back to original spec may be needed too ! Groan!!!
 

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If it was a dealer fit option, it's possible that the van was ordered from the factory wirth Towbar Prep. If so you should not need to be cutting wires - it should just unplug at the rear of the van. IIRC you can tell if it has Towbar Prep from the PR code list.
 

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As far as I know the PR codes (label under dash drivers side or in service book) go

1DO No towbar prep
1D7 With prep
1D1 With fixed factory towbar (see mine below)
1D7 With factory removable tow ball

CAN wires are easy to spot always being twisted pairs.

Maybe yours is a 1DO and you cut the wires for the dash indicator for the 'towbar plugged in'?

 

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Discussion Starter #9
Great stuff thank you for the pics...I have been searching for a build data sticker but haven't been able to locate one yet...I didn't get the original bookpack it was a duplicate...and no sticker under the dash found yet !

I have just had a very quick look, the towbar connection kit is a trailer connection kit by right connections...also there were 3 wires that I cut in the engine bay that go up behind the dash. 2 are orange with stripes so probably canbus and the other is black red.

Is canbus a separate box or are the wires likely to tap into the fusebox to connect to canbus ?

Thanks again for all the input so far I will keep posting my findings in the hope they may proof useful for anyone else.
 

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They vary year to year, but typically the towbar controller (which is a CANbus connected module) should be near the battery - it is on mine. The CANbus wires probably tap in near the main BCM. AFAIK there are no fuses on the CAN network (it's designed to tolerate as much main battery +ve as you can throw at it, as well as straight short to earth).
 

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My t5.1 is an ex Mercedes recovery assistance van
How cool is that, is that a real thing? Oh the irony! If only I had a pic of your van in its previous livery, preferably towing a broken down Sprinter... :D

AFAIK there are only two places for the PR label, the one under the dash should be directly above your ankles (no dismantling needed). You could try rocking up at your local dealer with your VIN and charm them (tell them the Merc history!) and maybe they will give you a print out of the original details. They can only say no (and try and sell you new van).

If your van was a basic (Mercedes LOL:) spec version it may not even have a trailer controller. If you have access to VCDS you could see if it finds it diagnostically but there is no guarantee that it will communicate anyway if wires have been cut here and there.
 

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Discussion Starter #13
Traced the 3 wires that came from the trailer connection kit loom into the van from engine compartment...there were 2 orange that connected to can bus feed and one black red that I guess was indicator ? Anyway removing them completely from the equation has made no difference...my next plan of attack will have to be with vcds I guess to check the trailer settings ?

Would the Carista dongle and app be capable of changing trailer settings ?

Just to recap everything works normally apart from the dashboard indicators flash at double speed and bulb failure light still on !
 

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The PR code label on a T5.1 if it's survived should be on the drivers seat base, behind your ankles.
 

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Discussion Starter #15
Hmm have searched for the build code stickers...no sign of any yet was hoping they would be under the dash...will try the seat base but I have had the seat off and don't recall seeing a code sticker !

Thanks for the assistance so far !
 
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