ABS Warning light

[matt5791]

Was driving thrtough the Alps last week and on the autoroute across France the abs and esp warning lights came on. Then the next day, they were not on initially, but then suddenly back on, but also a big red warning light in the centre screen this time.

The abs is not working (its not lying) but obviously full braking power maintained. The manual says drive carefully to a dealer, but that wasn't really practical.

Anyone got any ideas on this - I had the rear brakes rebuilt not so long ago, and I was wondering if a loose sensor cable was to blame?

A8 3.7 Quattro sport 2000 year.

Many thanks for any help

Matt

[NickGUK]

The light being on simply means there is a problem and the ABS is currently off, but as you said Full braking is still available. The ESP light is on to as its linked with the ABS system.

Ok, you have 2 options, if you have vag-com, then simply interogate the ABS ECU and that will tell you.

alternatively check all the wiring etc at all 4 wheels, remove and clean the plugs on the ABS sensors, see if that fixes it, if not remove the sensors themselves and ensure the ABS sensors themselves are clean at the "sense" end.

If that still fails to put the light out, and you dont have VAG-COM, then simply disconnect each sensor in turn, and use a multimeter to measure the resistance in kohms across each one in turn and "if" its a dud sensor, then one that is dud will give a vastly higher or lower reading to the other 3.

I cannot remember the exact readings you will get, but you will def see which one is fooked.

[matt5791]

UPDATE

I currently have the car in at Listers Audi in Coventry, and they have been replacing the front disks and pads, plus one caliper which they told me had been binding and taken out the ABS sensor.

After two days they now say that the ABS ECU has a fault and they want to replace it with a new one (£1000 fitted).

Does anyone have any suggestions here, or do I just get them to do it?

I am picking the car up later anyway because it (the ECU) will need ordering in and thet will take a week.

Very grateful for any help,

Matt.

[ronmcl]

I'd definately want a second opinion before going ahead. Others here know better than me, but I've always thought the ECU box was the most reliable bit - it's far more likely to be the remote stuff that hangs off the end of it. Defo worth being sure that they are all 100% before commiting to a £1k bill.

[LostKiwi]

I'd second that. In my opinion (and bear in mind I'm no expert) the parts most likely to fail will be wiring between the body and the wheel and the sensors themselves. Audipages have an excellent article on how to test the wires and repairing them when you find a duff one. In general electronice seem to be pretty bullet proof (how many people have you heard of with a duff ECU?) so I would look for all the mechanical answers first... especially if there's a grand at stake!!!

[GlynH]

[ QUOTE ]

UPDATE

I currently have the car in at Listers Audi in Coventry, and they have been replacing the front disks and pads, plus one caliper which they told me had been binding and taken out the ABS sensor.

After two days they now say that the ABS ECU has a fault and they want to replace it with a new one (£1000 fitted).

Does anyone have any suggestions here, or do I just get them to do it?

I am picking the car up later anyway because it (the ECU) will need ordering in and thet will take a week.

Very grateful for any help,

Matt.

[/ QUOTE ]

So did it really need the discs, pads & caliper replacing?

[Ska]

If the brakes were binding then yes but the Speed sensor wires can be responsible for turning on the ABS light. HAppened to me replaced sensors from IT_S8 and they're fine now but there is a tell tale sign in most cases where the sensor is at fualt. This is in the form of a jerky hesitancy by the car at almost crawling speeds; almost as if the ABS were kicking in. New sensors cost aroun £90 each and its almost always the front ones. Does the car jerk at low speed i.e. 0-5mph? If so then it is almost defo the wires

[matt5791]

Thanks for all the help.

Firsly, I did infact say to them that I was under the impression that the ECU woudl be reliable - afterall it is just solid state electronics in a box, probably positioned inside the car body somewhere isolated from the rigours of the engin bay etc.

Secondly, the car performs faultlessly other than the ABS is not working - ie no jerky behaviour.

Thirdly - the pads and disks (well certainly the disks) were well past their sell by date - so no problems with that.

What has just occured to me is that I actually have a warranty for this car! - which I am pretty certain covers ECU's.

I will probably get a second opinion anyway though.

Matt

[IT_S8]

[ QUOTE ]

What has just occured to me is that I actually have a warranty for this car! - which I am pretty certain covers ECU's.

Matt

[/ QUOTE ]

If its under any sort of warranty, great, get it done by Audi and get your moneys worth - If not, then depending on what year / model car you have, I may be able to help with a second hand ECU at a fraction of that cost....

Ian

[matt5791]

Ok - many thanks indeed for that.

Matt

[matt5791]

Turns out ECU's are excluded under the warranty! Bugger.

Anyone know a reputable specalist - I am in the Midlands, but will travel a bit.

Thanks,

Matt

[Ska]

The ABS module is located in the black box near the bulkhead (rear rhs if looking at the engine bay from font). The seal on that box is a load of to55 so you might get water ingress. Have a look to see if there is any water marks inside the box indicated by whitish marks.

Have you got VAGcom? some codes would tell you more; what did the stealer give you as an indication to the modules fault i.e. is it dead full stop or they cant communicate with it etc.

When it comes to a potentially big cost scenario for me I eradicate all of the smaller potential causes first; If I were you I'd pull those sensors and have a look at 'em. Stealers don't have or don't use their instinct or intelligence from my experience; its a simple case of plug it in to the VAS diagnostic and do what the machine says. They probably won’t even guarantee you that replacing the module will fix the problem.

Check those sensors it’s dead easy to just whip off the wheel and pull them out. And the car doesn't nessessarily have to jerk at low speeds, if the wire is broken internaly then turning the steering wheel can set of the ABS warning light with the Bid red sign on the DIS. If its still messing around then I'd take up IT_S8's offer as I cant see a new one costing anything cheaper than £800. Though there are a few ECU doctors around who say they can repair the units for around £150 but you'll be with out a car whilst they repair it.

Hope you get it sorted

[LostKiwi]

You could always try here - a bit cheaper I think?

[thenamesross]

My A4 has the same probs and its the ECU thats knacked. Im going to send it off to the place LostKiwi mentions (once I get round to it). Apparently this is a common failure with the ABS. My old S4 had the same issue and it cost the owner about a grand for a new one.

From asking around it tends to be the ecu that fails rather than the pump. The ecu comes off easily and bba-reman refurb it for you.

Best to pull the codes 1st to narrow it down a bit.

[IT_S8]

[ QUOTE ]

Anyone know a reputable specalist - I am in the Midlands, but will travel a bit.

[/ QUOTE ]

I'm not a specialist, and not quite up the master level of Ska and Nik, but I dont charge either If you fancy a trip up to Harrogate, I can whip out the Vagcom, check the errors, take a look at the ABS sensors etc for nowt.... At least then you might have more confidence in what bits need changing. ABS sensors are most likely - they're a sod, ESP relies on ABS, so any fault with ABS turns off ABS, then ESP goes off too, and before you know it your dash looks like an xmas tree all down to one sensor....

5 minute job to whip the wheel off an check out the sensor, but to be honest, Vagcom should tell us everything we need to know before we go near a spanner...