abs light

pc.blogs · Post by **pc.blogs** » 30 Sep 2002, 03:22

my 96 xantia abs light stays on when starting and usually goes off after a few miles. diagnostic check could not communicate with the ecu. i replaced sensors at my last mot(6000 miles ago). i am told the ecu is at fault but i am not so sure. is there a way of testing the system without the use of specialist testing gear. could anybody tell me where i can get a wiring diagram for the braking circuits.
many thanks.

alan s · Post by **alan s** » 30 Sep 2002, 04:23

There have been quite a few threads on ABS in particular Xantia ABS so if you go to "search" and put either "ABS" or "Brakes" in I think you'd get plenty of advice to read on this subject.
To me, it sounds more like something not telling the ECU that it's supposed to be working rather than it not working! I'd personally begin bt removing the road wheels and giving the serrated wheels that teh sensors work on a real good cleaning and if that didn't work, I'd try replacing the relays associated with the ABS before I got too excited about an ECU. We have been told by those in the know that ABS - ECUs are ultra reliable & your chances of simply blowing one is on par with being struck by lightening. The fact that the system does work after a short while to me almost takes the ECU out of the equation.
Alan S

Post by **n/a** » 30 Sep 2002, 04:56

there ar a few systemes used on cits ie:- bosh 2e, teves, bosh and bendix i would need to know which of these your auto has so i can check the autodata book , but i do agree with the last post and it is not the ECU i think its air in the system which is explained very well in the heains manuel or rust/dirt/grease build up on the toothed rings these are found on each wheel next to the sensors common fault with all ABS no matter what car
DAVE

gjb02 · Post by **gjb02** » 30 Sep 2002, 14:48

The toothed wheel/ serrated wheel, is actually called a phonic wheel, the inductive pickup (abs sensor) recieves a low induced a/c signal voltage as the wheel rotates. To work correctly the pickup relies on a small airgap,(this should be in the specs of the Haynes book of lies). With corrosion this airgap can increase to a point where little or no signal voltage is produced, this can in turn cause the ABS fault light to illuminate. This happens because the ecu, can't see that wheel moving, and because the brake switch isn't pressed, it can't figure it out (logic circuits), so, bingo - fault light. If the cars covered a few miles it could be corrosion, other than that as suggested previously, clean them up. It has been mentioned before about incorrectly routed sensor cables. I recently had one on a BX, the tyre wall had rubbed the cable 3/4 through breaking the connection but not the cable. Always something to look for.
Gareth

gjb02 · Post by **gjb02** » 30 Sep 2002, 21:29

Dave, I only use the terminology to try and increase peoples understanding of systems. It's all very well giving the,'mate down the pub speak', when giving forum members advice on what there problems may be, and how to fix them, but other people read these forums, they may want more information of a more technical nature. Well they might, knowledge is power, try to part with some and help people out, A + B might = C but it ain't worth s#?t if you don't know what B is! No, I'm not taking any medication<img src=icon_smile_big.gif border=0 align=middle>
Gareth
Edited by - gjb02 on 30 Sep 2002 16:30:39

pc.blogs · Post by **pc.blogs** » 30 Sep 2002, 23:10

forgive me for not being an expert but am i right in thinking that even if fault diagnostic tools can't communicate with the ecu that it is not necessarily the ecu at fault. if so how can i check for the offending sensor or wiring problem

spanners · Post by **spanners** » 01 Oct 2002, 05:00

i have usually found that the test equipment has always worked for me unless i have faulty ECU or fault present on diagnostic line to ECU i think pin 13 is the one in 30 pin plug. does it just not read fault codes or can you do modulator tests (i,m guessing you have tevas system.)

mg46783 · Post by **mg46783** » 01 Oct 2002, 05:18

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
my 96 xantia abs light stays on when starting and usually goes off after a few miles. diagnostic check could not communicate with the ecu. i replaced sensors at my last mot(6000 miles ago). i am told the ecu is at fault but i am not so sure. is there a way of testing the system without the use of specialist testing gear. could anybody tell me where i can get a wiring diagram for the braking circuits.
many thanks.
>> Its unlikely to be an ECU (abs ecu ) fault - but its not unheard of. Your abs ecu is seperate to your ems ecu and shouldnt be confused with same. It is a 37 pin Ecu if its the one Im thinking of - I would suggest you check the earths associated with the ecu and then go to checking your supplies . It doesnt sound like a supply problem as you do have a light but a dicky earth can send the system barmy. Pin 24 is your abs ecu earth - and its worth noting that Pin 16 is your MIL light - check... Pin 22 is your input from your brake light switch... have you checked yolur brake lights work?! Sounds stupid - but beleive me, it can save hours if all it was waa a faulty brake light switch throwing the ecu. Theres more - but see how you go with that!

<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

chrisswan · Post by **chrisswan** » 01 Oct 2002, 17:55

xantia abs problem is very common. if you cannot communicate it is 99% likely the controller. Teves make 2 systems. go to www.bba-reman.com for more info

Post by **Jon** » 01 Oct 2002, 18:29

not THE Chris Swan?
Jon Wood
IT Supervisor
GSF t/as Andyspares

chrisswan · Post by **chrisswan** » 01 Oct 2002, 19:11

not the one who ran finelist, no! i'm younger and better looking

pc.blogs · Post by **pc.blogs** » 01 Oct 2002, 23:04

today i checked all wiring connections at the 37 pin plug and all readings are ok. also the abs relay is working ok. can i assume my ecu is knackered?

chrisswan · Post by **chrisswan** » 01 Oct 2002, 23:29

its 99.9% certain
ps andyspares, did finelist take you for a lot? they only got us to the tune og £2000 through lucas service chain

alan s · Post by **alan s** » 02 Oct 2002, 03:22

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
today i checked all wiring connections at the 37 pin plug and all readings are ok. also the abs relay is working ok. can i assume my ecu is knackered?

<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>
Have you cleaned the sensors & serrated wheels yet? If not I'd suggest doing that before you go giving yourself a heart attack (normally associated with customer receiving the price of an ECU from Citroen<img src=icon_smile_shock.gif border=0 align=middle> I would also follow through on the suggestion regarding earthing. The reason I keep harping on cleaning these things is that I had a similar experience on my BX. I used "Electronic contact cleaner" on mine but WD40 I would imagine would be just as effective. I'm a bit iffy about degreasers as some are water based.
Alan S