Electrical nightmare - RHS - speed sensor - SOLVED

T6 Sam

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Hi Guys

Got a bit a bit of a problem with my T6 Kombi and a bit lost as to what to try/check next. I'll give you the full story in case there is something obvious that i have done to cause this issue.

Couple of years ago I put silent coat down over the rear floor of the van along with the sides, sliders, boot and roof. Couple with closed cell foam and thermofleece it made a huge difference to the way the van sounded. Also installed a couple of rear usb charging ports on the b pillars and a 12v power socket in the side panel of the boot. Carpet lined the van as well for good measure (what a difference that made). Drove from Scotland to France last year for a ski holiday and it was great. Even got adaptive cruise activated prior to the holiday and it was fantastic. Van had been fine since.

However, i got greedy with wanting the van to be as quiet as possible, and prior to a ski trip this year, i decided that i was going to silent coat the front floor and put down some carpeting. So a couple of months ago out came the back seats and some carpet went down in the back (Just a cheap offcut from local carpet shop). Fitted it on top of the rubber flooring mat and now the van was noticibly quieter again. Then on sunday 25th feb out came the front seats (didnt realise at the time i could just unscrew the connector block holder so unplugged them all), lifted up the rubber flooring and put down the silent coat sheets, Put the rubber mat back down, then cut some carpet for the fron so that it would join with the carpetting in the rear, and the front was cut using my existing mats as a template so that it wouldnt bulge or anything on the wheel wells or the central bump under the gear lever. Seats went back in, connectors were reattached and on driving the van i marvelled at my own magnificence at how quiet the van was and how smooth the upcoming road trip was going to be. (i had noticed a couple of months ago that the rear 12v power outlet was no longer working but i put this down to being a cheap ebay/amazon outlet and something to be replaced at a later date - fuse appears to be ok). I used the van on the monday and all was fine, tuesday came and went and no issues, fueled the van up and cleaned it top to bottom ready for our trip on the thursday. Wednesday the van didnt move as it was being packed and on thursday daytime it got a final wash and snowfoam ceramix coat to help the screen stay clear as rain was due to hit on the way to the chunnel. i also pulled out the passenger for light bulb, and stuck a rod in there with some shop rag to clean up some condensation from inside the light unit. Everyone gets in the van, started her up and..........abs light, traction control light and tyre pressure light all on. No cruise control, no abs and no traction control.....this was not looking good.

We left for our holiday and drove down to the chunnel. At a service station we stopped, and on starting the van back up the warning lights were off........but as soon as we started moving the errors all came back up again. Ignition off again and the lights were off ( i popped my headlights into tourist mode as the option to adjust them isnt there when the abs/tc/tp lights are on), but again as i moved the errors came back. Fast forward a train journey and 200 miles into france and we stopped again. This time, on starting back up the warning lights were off but stayed off and i had my cruise control back again. Those were a few hundred glorious miles with the adaptive cruise working as it should and all was well again.....until we got to our overnight stopover.....as soon as we stopped i turned the ignition off then back on again and the warning lights popped back up. And they stayed on for the rest of the journey the next day, and our whole return journey on saturday and yesterday.

Having checked with Carista, i was getting a warning about the right hand side rear speed sensor having an electrical fault, and assumed the issue was a bad sensor. So i picked up a new Bosch sensor from Eurocarparts this mornign and set about fitting it. Took longer than expected as the old one was pretty much welded in place but eventually managed to drill and removed the old one and put the new one in and connected it. Back wheel back on.....keys turned on.....and the errors stayed lit up on the dash. Checked again with Carista and the issue is still showing as rear RHS sensor - electrical issue. So i guess the issue was not the sensor itself.

What I've done so far since is take both seats out and the front carpet, check all the connectors and they are fine. If i unplug the T17f connector and turn the ingition on, Carista shows me errors for rear left and rear right speed sensors, both stating electrical error , when i reconnect the plug and try to clear the codes the left one clears but the right one always comes back straight away. I have check the continuity of the female half of the plug for left and right sensor wire and they both appear to be fine (I'm assuming the female haf of the plug is what goes to the ecu etc as the cable appears to be routed to the front, and the loom attached to the male plug appears to run up the b pillar on the passenger side) but i cannot seem to get a reading from the male half of the plug for either sensor (could just be a poor connection for my multimeter - not sure). But the left sensor is definitely seen when the plugs are connected. Carista live data also shows speed readings from the front 2 wheels and the rear left but nothing from the rear right. I took the new sensor back out and tested that for continuity and got a reading on that so the sensor would appear to be ok.

My question now is does this seem like something i have done to cause this? (the timing seems too coincidental). Are there any connector blocks inside the van at the back that i can take apart and test for continuity....or is there something more obvious that i am missing and should be checking?

Any help or advice would be very much appreciated

thanks
Sam
 
Hi,

There are no further connectors in between T17f and the sensor plug. Look at page 4 of wiring diagrams at T6 - ABS Anti Lock Braking System Wiring Diagram - rear right sensor is at pins 2 (brown) and 3 (black) of T17f.

The loom routing can be seen from Rear Right ABS (speed) sensor short circuit [Resolved] - it's unlikely that you would have disturbed the loom in any other location besides the seat base.

Are you sure the error code was exactly the same with the old and new sensor? The reason I'm asking it's easy to get a wrong part number for these sensors. There's unidirectional and bidirectional variants available, and unidirectional is the correct one. With wrong part error in VCDS says "Incorrect component installed" but not sure how it would show on Carista.
 
Hi,

There are no further connectors in between T17f and the sensor plug. Look at page 4 of wiring diagrams at T6 - ABS Anti Lock Braking System Wiring Diagram - rear right sensor is at pins 2 (brown) and 3 (black) of T17f.

The loom routing can be seen from Rear Right ABS (speed) sensor short circuit [Resolved] - it's unlikely that you would have disturbed the loom in any other location besides the seat base.

Are you sure the error code was exactly the same with the old and new sensor? The reason I'm asking it's easy to get a wrong part number for these sensors. There's unidirectional and bidirectional variants available, and unidirectional is the correct one. With wrong part error in VCDS says "Incorrect component installed" but not sure how it would show on Carista.
Yeah its exactly the same message i got for old and new (electrical error & manufacturer specific code 00088). However, i get the same message for the left one (different code number though) if i disconnect T17f, so it suggests that it cant communicate with or see the new one (hence me thinking i have a wiring issue). Carista info is quite basic, bit of an issue not having VCDS.

As an aside, the new sensor is a bosch 0986594505 - not sure if this is bi or uni-directional.
 
New part (vwht003856d) ordered from VW and fitted today, still getting the same error message from carista and same lights on the dash so looking like the sensor is not the issue. Is it worth running a couple of wires from the sensor straight into the T17f plug to rule out the wiring at the back of the van?
 
Might be worth checking the grounds in the area as well as the +12v side
 
Sounds like a wiring fault indeed.

Continuity checks between T17f/2 and sensor connector pin 1 (brown) and T17f/3 and sensor connector pin 2 (black) would be in order.

Another idea would be to temporarily depin and swap T17f/2 <-> T17f/9 and T17f/3 <-> T17f/10. This swaps the rear left and right sensors between each other. If the DTC jumps from right to left you know the fault is in between T17f and the sensor. If the DTC stays on the right side you know the fault is in between T17f and ABS module.

But I still believe most likely the issue is somewhere in or close to the passenger seat base as that's the area you've been working on.


1710335614387.png
 
Thanks guys, appreciate the feedback. I will try depinning and swapping and will see if the error switches sides. Will keep you posted.
 
Off topic but an interesting observation from above wiring diagram: look at the G46 wiring from ABS module and how wires switch colours at T10k. Not sure but I think probably the sensors don't really have a polarity and swapping the wires swaps the direction?
 
Always a possibility. I depinned and swapped the left and right wires and......the van now tells me I have a left rear wheel speed sensor issue. Put the cables back to the way they should be and I have a right rear wheel speed issue. So the cable has an issue somewhere between the sensor and the T17f connector
 
Always a possibility. I depinned and swapped the left and right wires and......the van now tells me I have a left rear wheel speed sensor issue. Put the cables back to the way they should be and I have a right rear wheel speed issue. So the cable has an issue somewhere between the sensor and the T17f connector


Well, at least that narrowed down the area a bit. Unfortunately there's no more connectors en route to the sensor so can't do any midway checks at least without interfering with the wiring. Since you have the seat removed I would inspect the red square area in below image (under the seat up to the base of B pillar) carefully for any damage, as well as from near the connector at the other end.

Beyond that, I think the easiest though still very tedious would be to just identify which of the two wires is at fault and run a new one (+ couple of spares for future faults or rear dashcam or whatever) all the way through. Probably the effort to find the exact location of the fault is way more work than just running a new one. That is, unless someone knows a cheap and smart cable radar or something that can identify wire fault distance from the cable end...


1710352650851.png
 
I know of cable testers that can measure breaks on cat5/6 type cables, but they tend to only be accurate to a few meters.

You can get ones that inject an RF signal that you can trace accurately, but you have to be quite near the wire which probably doesn't help in this situation.
 
Thanks guys, I've ran out of light tonight with getting the kids to bed and back at work now after holidays so will be a few more days before I can look further at it. Will check out that highlighted area first and work back a little. If nothing there then I'll probably need to look at running an entire new cable or 2 as I've picked up 7m of red and 7m of black cable from Halfords for it. Any ideas what the connector type is call that clips onto the sensor in case I need a new one of them
 
There will be a part number on the connector for the abs sensor, best bet is getting the number from it and googling.
 
Hi folks, just wanted to say a big thank you to everyone who provided some input.

I spent a couple of hours today checking wires for continuity from the T17f connector to the top of the b-pillar, then from the b-pillar to just behind the rear seats, then to above the tailgate, and then to just before it disappears out through the grommet to the exterior of the van. Cables were fine to all the way back here.

Checking continuity from just before it went outside to the abs sensor plug showed that the ground/signal wire was fine, but there was no circuit on the 12v. Quick bypass cable attached and then ignition on had the ABS/TC lights going out as normal. So ran a cable through for 12V, soldered it to where i knew the cable inside the van was good, and soldered the other end to the cable coming out the plug. A bit of self-amalgamating tape later to seal it up and protect it from the elements and put the rest of the van back together and i now have a fully working van with the error codes now cleared :)

Thanks again guys, i couldnt have done it without you and your knowledge/insight :)
 
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