Warning light not illuminating on dash when ignition is switched on.
But when main wiring harness is disconnected from abs module warning light illuminates.
ABS module has been to specialist reparer and has checked out ok.
Also diagnostic equipment has been unable to link with ecu both at the specialist and by two other systems.
As of yet I have not taken car to the agents?
Any help or ideas would be very welcome.
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wagon man
The ABS light can be wired to fail safe. If the display module loses contact with the ABS ECU it will put the light on; it needs a connexion to the ABS to keep it off. If it's not coming on at key-on; doing it's self-test and then extinguishing; there's likely a problem with the feed or earth of the ABS ECU.
If there's no comms with the ABS; can the scanner get into all the other systems? If not; has a non-standard radio been fitted?
If it can and it's just the ABS that's unresponsive; then check the various fuses [fuse 7 is the ECU feed] and the earth connectors.
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If it's not coming on at key-on; doing it's self-test and then extinguishing; there's likely a problem with the feed or earth of the ABS ECU.
This is exactly what is happening, the fuses both on the side of the dash upto the o/s door and the ones under the scuttle panel on the o/s all test ok.
Were is the earth gained from and is it possible to test this by fitting a temp earth feed to the ecu
and what colour is the earth wire,
I havent tried to get into any of the other systems.
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The earth wire will be brown and from pin 19 on the plug. It'll likely end up either on the engine, or on the main battery cable earth point under the bonnet.
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I am expecting the unit back from the specialist tomorrow.
I will look at the wiring tonight. thankyou. hopfully i will find the fault I will keep you informed if thats ok,
John
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With the ECU fitted, does the ABS work, regardless of what the warning light shows?
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Hi David,
That is the one thing I did'nt try before the unit was sent away to the specialist. (it failed the M.O.T because the light failed to come on go out after
2-3 seconds)
I have just re-fitted it to the car tonight but not bleed the system yet.
The a.b.s light seems to do exactly the same as it did before.
Do you have any solutions to my problem.
thanks John
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Hi Screwloose,
Still no joy with this a.b.s. found the earth point as you said cleaned it up it was'nt that bad to be truthfull. checked fuse 7 all ok checked for a feed in the fuse box all ok. when I take out fuse 7 with the ignition on the a.b.s light on the dash comes one and will stay on untill the fuse is pushed back in.
(I have not yet bleed the system though. i dont think that makes any differance to the warning light test)
Hope you have not run out of ideas yet.
would it be possible to speak direct to you on this problem ?.
thanks John
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John
It's always best to keep things on the forum, so that they're accessible to future searchers.
I've not run out of ideas; but I do now wonder about that ABS controller - did they test it specifically for a communications error?
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what is being used for the diagnostics - it is vagcom or bosch not a generic tester isnt it? Vag use a specific protocol.
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Surely the whole point of the OBD specification is to allow any generic reader to be able to extract fault codes? Obviously VAG-COM required to actually do complicated stuff.
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yes but
car is 9 years old - wouldnt be eobd anyway I dont think.
fault is abs not engine - you need something that can talk to the abs controller
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>>Surely the whole point of the OBD specification...
Yes, and it's fine for very basic emissions related engine fault codes. There's absolutely no harmonisation between all the different transmission, ABS, ASR, etc., etc. systems that could also be fitted to different vehicles. The lack of standards makes any attempt at kitting up for general electronic diagnosis prohibitively expensive - just the way the manufacturers like it!
Number_Cruncher
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The lack of standards makes any attempt at kitting up for general electronic diagnosis prohibitively expensive - just the way the manufacturers like it!
NC
Tell me about it! Only an idiot would get into this game now. It's all over.
If everything goes to plan [?] by this time next week I'm out of this manic business and the proud owner of a nice Telford-built stone pier 30 miles from anywhere. I can potter about fixing that up and I won't miss cars one little bit!
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Hi Screwloose,
The specialist company I sent the unit is located in Kent, When I spoke to there engineer about the fault he said that all tests results on my unit came back ok.
but when I asked the question about not being able to communicate with the
a b s, e c u he said they were unable to communicate also with it,
At this point he went and tested the exact same unit in there stores and came back to me to say that he was unable to communicate whith that unit also, but the test results were the same as mine, but could'nt give me an explanation of why. He offered to lend me there unit of the shelf but I could'nt see the point if both units tested the same !!.
So thats the story to date, I also phoned the Audi dealership to-day to see if they could help or give advice, no advice only that it would cost £108.00/hr to diagnose the fault,
John
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John
The company in Kent sounds like BBA at Gillingham. It might be worth plugging in their loan unit to see if this is just a comms error on yours. Odd that theirs wouldn't talk either?
It would also be worthwhile finding a piece of grass or gravel and seeing if the ABS is actually functional. [You'll probably need to be going at over 10mph.]
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Hi screwloose,
you are right with BBA at Gillingham, First time I have used them though, I know of other garages who sent items for repair and they have been ok.
Bleed brakes tonight took car out for test run and NO the A.B.S dose'nt work,
to be honist with you I did'nt expexpect it to.
Any further ideas will be welcome,
It may be time I packed this job in like you (I have been in the trade for more than 30 yrs mainly in the heavy commercial side) it may be a case of you cant teach an old dog new tricks ??. with all this electronic's that are involved to-day.
I look forward to your reply.
John
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John
As it isn't working either; [I was half expecting it to operate] then this appears to be more than a comms error. Take BBA up on that loan unit offer. These do suffer from mounting stress faults; [levering the ECU with a screwdriver against the modulator block often causes the light to flicker on affected units] so it's possible for it to bench test OK, but not function when installed.
If the radio is definitely the factory-fitted unit [it matters] then the next step is a pin-by-pin slog through the ECU plug testing every one for the correct pedal switch signals, resistances, voltages, data, etc.
The wiring diagram is on Autodata's CD if you can access it. Also plug in a scan-tool and investigate if the engine ECU is still getting speed info from the ABS and talk to the instrument/display ECU for anything useful it can tell you.
Old dogs pick up the rudiments of electronic fault-finding more readily than computer-savvy youngsters. The hard-earned rules of diagnosis are universal. The procedure for finding a misfire on a points system is identical to tracing a complex CAN-Bus fault; only the systems under test are different.
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Hi Screwloose,
Latest developments, tried the screwdriver levering the e.c.u against the modulator body no success, I took the chance and purchased a second hand e.c.u unit plugged it in and bingo the a.b.s warning light lit on the ignition test but failed to go out after about 2-3 seconds, so plugged the the scanner in and it communicated with the e.c.u and came up with o/s/r wheel sensor u/s so tuesday i will change that and see if all is ok.
I will let you know the final outcome,
John
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