Hi all, this is a question I've likely already answered myself. I've had a recurring ABS and ESP amber light that I hoped I'd fix by fitting a new O/S sensor that had rubbed on the anti roll bar, it did extinguish the lights but when taking the car for a test drive the lights have come back on. So I've had the laptop out so I could get into vcds-lite to see what the abs module was recording the fault as, it indicates that there is a voltage issue from the electronic brake booster. Now from doing a bit of reading I understand that there is a solenoid on the servo that gives extra assistance, this then has a wire that goes over to the ABS pump. I believe the fault lies in the signal carried by this wire.
Has anyone else experience with this fault?
Being the Vr6 it's close to impossible to get to the brake fluid reservoir let alone the master cylinder/servo, I can't even see the offending wire. Has anyone any advice on how I can get enough access to this wire or should I be looking at the other end where it joins to the pump?
I've tried to identify what is triggering the fault but it appears random, driving I notice no difference to the braking feel.
What is very peculiar is that when the warning lights come on there is a change to the mapping of the gearbox, it becomes later to change up through the gears and really noticeably hangs onto a gear longer. I don't see why an ABS fault would require the car to use higher revs that changing up later provides?

Can't answer your question about the likely fault but the abs and transmission do talk. I would think the abs is requesting it to stay in a lower gear for engine braking purposes

I think I'm just of an old man school mindset, I hadn't realised the electronics were quite that advanced 20 years ago, I know that the jatco automatic transmission was one of the first to have fully independent electronic control. What I'm having to learn is how the separate systems communicate to each other then alter their parameters, as for this fault I think it is going to be a bit of a headache.

It's mind boggling really, I do a lot of faffing with BMWs and the amount of can bus systems on those with all the modules talking to each other is madness.

It's incredible to consider the amount of data that a modern car is handling, just the emissions control system must be vast. Back to the ABS I've gone to work on today I'm keeping my fingers crossed that I've cracked it, at least after a 20 mile drive it's kept the lights off. For reference I decided that rather than taking that awkward engine undertray off then trying to reach up to the servo I took the air filter box out which actually gave good visibility and enough room to get a hand to it. Fortunately the solenoid sits under the end of the master cylinder too so it was relatively straight forward to get the wiring plug off, in fact doing so was too easy. The plug was on past the clip but compared to every other similar connector I've worked at it was a very loose fit, but after I had removed it I could not get the damned thing back on. I've no clue as to what changed but every attempt felt like I was about to bend the pins, in the end I had to just force it back on which I really don't like doing. But it's now on with a very tight fit and running through vcds all the faults are cleared and staying that way.
Mot next week and as far as I can see it has nothing obvious to fail it but I can only see so much from laying under it in a car park.

An update to the ABS issue, I spent another 4 hours trying to find an obvious fault with no luck. I was still struggling to find a fix that would allow me to get the light out long enough to go through the mot. In the end I had to give up and chance that it'd stay off during the test which it didn't so the car failed. But it initially failed on emissions which I had a feeling it may as a week after its test last year it had the catalytic converter stolen, in need of a quick fix I bought a relatively cheap one (£250) which I was aware didn't meet euro specifications. We did however manage to bring the emissions down to a level just below the limit to get a pass but then said abs light came on. The tester was very decent and said if I could bring the car back with the dash clear of warning lights then he'd give me the pass so back on the laptop I went, it's showing intermittent abs pump fault so I'm thinking the control module is beginning to fail. In the end I gave it a persuasive tap and off went the light, the car got its mot and that offending light has stayed off since then plus I've covered about 160 miles since. So for now that's it I'm done getting cold and frustrated at it, I'd rather just enjoy driving it until the weather picks up then I'll get to the bottom of the problem. Thanks all.

Yes, this cold weather isn't much fun, certainly not fun enough to be lying on the floor looking up into wheel arches and the like.

It's worth getting this sorted, although in the meantime driving more carefully. Make sure you take plenty of care out there, the roads are like the Law of The Jungle these days