ABS fault. Help needed please!

BX Tech talk
User avatar
deltic
BXpert
BXpert
Posts: 607
Joined: Tue Jan 25, 2011 10:48 pm
x 9

ABS fault. Help needed please!

Post by deltic » Sun Nov 22, 2015 5:24 pm

Not long after my rear wheel bearings were replaced GTi's ABS light is now on with the garage reporting no obvious problems relating to their repair works, but saying that they would need to bring in an electrical engineer to check things through more thoroughly. With the MOT looming and me doubting the garage's ability to be able to establish what the real fault is I need to find an alternative solution.

I'm based in north west Kent - would anyone be able to suggest someone locally competent to do the work? Failing that would anyone on here like to take on the challenge? Prepared to travel if needs be and of course will pay a reasonable rate. PM me if you prefer.

Thanks in anticipation.
1991 BX GTi Auto, grey, 133,000 miles (2015 & 2017 Citroen Classic Challenge veteran)
2006 C4 VTR+ 2.0 Coupé, silver, 60,000 miles

User avatar
ken newbold
Over 2k
Posts: 4408
Joined: Sun Aug 14, 2005 10:53 pm
x 5

Re: ABS fault. Help needed please!

Post by ken newbold » Sun Nov 22, 2015 7:00 pm

Most likely one of your rear sensors has gone, a dodle to change and just as easy to find the problem. I don't have the method to hand and it's been so long since I did any I can't remember but fairly sure it's in one of the haynes books. The ABS ECU is under the passenger seat. You'd need a cheap ohms/multimeter and the rest is just a case of measuring the resistance across the pins to each sensor. Not sure how easy the sensors are to get hold of now although Xantia ones might do.
They think it's all over, it is now!

User avatar
Way2go
Over 2k
Posts: 7279
Joined: Fri Jan 13, 2006 3:15 pm
Location: RCoBerkshire
x 2

Re: ABS fault. Help needed please!

Post by Way2go » Sun Nov 22, 2015 7:22 pm

Do you have a multimeter? If so, a good place to start is to measure the pick-up sensors electrical resistance at each wheel. For initial tests rather than get mucky at the wheels, disconnect them from the ABS "Brain" under the passenger seat and measure the Ohms for each one. The reading for each sensor should be similar.

If you get an open circuit reading (or even s/c) reading here then go to the offending wheel, disconnect the sensor and measure it directly at its plug. If no change, then it is defective. If OK then check connections and wiring between sensor and control unit.

The ABS connections are shown in Haynes diagram 6 circuit IV on page 13*49

Although the Cit stealer will no longer provide the sensors, I believe some on here have sourced Pug/other units that fit but require a change of plug.


Edit:(Ken, you posted while I went to find Haynes to mention the info location. Thinking alike though... :D )
1991 BX19GTi Auto

User avatar
deltic
BXpert
BXpert
Posts: 607
Joined: Tue Jan 25, 2011 10:48 pm
x 9

Re: ABS fault. Help needed please!

Post by deltic » Sun Nov 22, 2015 9:52 pm

Thanks both, sounds relatively easy... Fortunately I do have a spare rear sensor (condition unknown) and ABS ECU I took off a scrap GTi in 2002. Would one of you remind me how to remove the seat base please?
1991 BX GTi Auto, grey, 133,000 miles (2015 & 2017 Citroen Classic Challenge veteran)
2006 C4 VTR+ 2.0 Coupé, silver, 60,000 miles

User avatar
ken newbold
Over 2k
Posts: 4408
Joined: Sun Aug 14, 2005 10:53 pm
x 5

Re: ABS fault. Help needed please!

Post by ken newbold » Sun Nov 22, 2015 11:01 pm

Look under the front of the seat and you'll see two wire clips from the seat cushion round the seat frame, pull them forward to release and lift upwards the seat cushion, you'll then see two rubber bands holding it, simply unclip them.

Test your spare sensor with your meter set on ohms, should read somewhere between 800 -1200 ohms from memory. I have known the cable to the sensor head fail as it's only co-axial cable (TV arial) stuff and if the wet gets in, it rots away the outer braiding, usually under the securing clip on the arm. With some nifty soldering a new cable can be installed.
They think it's all over, it is now!

User avatar
Jaba
1K Away
1K Away
Posts: 1432
Joined: Tue Jul 05, 2005 7:54 am
Location: Usually in the garage
x 16

Re: ABS fault. Help needed please!

Post by Jaba » Mon Nov 23, 2015 9:57 am

It sounds as though the garage have damaged one of the sensors while removing them or just strained the coax. Either way the easiest way to check is to lift the rear seat and find the connectors there, not at the ECU. Measuring them will tell you which one to change.
Try not to damage the one you are taking out as it may be that it just needs a new length of screened cable splicing in with solder as mentioned by Ken.

Usually they are rusted in place so I cut through the rear hub locating hole through which the sensor passes and spread the two sides of the cut to open up hole a bit. It can then be wiggled out intact.
The Joy of BX with just one Citroën to my name now. Will I sing Bye Bye to my GTI or will it be Till death us do part.

User avatar
deltic
BXpert
BXpert
Posts: 607
Joined: Tue Jan 25, 2011 10:48 pm
x 9

Re: ABS fault. Help needed please!

Post by deltic » Mon Nov 23, 2015 10:04 pm

ken newbold wrote:Look under the front of the seat and you'll see two wire clips from the seat cushion round the seat frame, pull them forward to release and lift upwards the seat cushion, you'll then see two rubber bands holding it, simply unclip them.

Test your spare sensor with your meter set on ohms, should read somewhere between 800 -1200 ohms from memory. I have known the cable to the sensor head fail as it's only co-axial cable (TV arial) stuff and if the wet gets in, it rots away the outer braiding, usually under the securing clip on the arm. With some nifty soldering a new cable can be installed.
Thanks Ken, presumably the ones on the car should also give 800-1200 ohms if they are working?
1991 BX GTi Auto, grey, 133,000 miles (2015 & 2017 Citroen Classic Challenge veteran)
2006 C4 VTR+ 2.0 Coupé, silver, 60,000 miles

User avatar
deltic
BXpert
BXpert
Posts: 607
Joined: Tue Jan 25, 2011 10:48 pm
x 9

Re: ABS fault. Help needed please!

Post by deltic » Mon Nov 23, 2015 10:10 pm

Jaba wrote:It sounds as though the garage have damaged one of the sensors while removing them or just strained the coax. Either way the easiest way to check is to lift the rear seat and find the connectors there, not at the ECU. Measuring them will tell you which one to change.
Try not to damage the one you are taking out as it may be that it just needs a new length of screened cable splicing in with solder as mentioned by Ken.

Usually they are rusted in place so I cut through the rear hub locating hole through which the sensor passes and spread the two sides of the cut to open up hole a bit. It can then be wiggled out intact.
Or could it be that non-ABS wheel bearing have been fitted? Is that possible? That said the ABS was working when I picked the car up and on one occasion after that... I did check around under the rear seat and nothing seemed amiss. I'll try to check around this coming weekend and report back.
1991 BX GTi Auto, grey, 133,000 miles (2015 & 2017 Citroen Classic Challenge veteran)
2006 C4 VTR+ 2.0 Coupé, silver, 60,000 miles

User avatar
ken newbold
Over 2k
Posts: 4408
Joined: Sun Aug 14, 2005 10:53 pm
x 5

Re: ABS fault. Help needed please!

Post by ken newbold » Tue Nov 24, 2015 12:20 am

The rear sensors plug in under the rear seat, unplug them there and test each one, easipeasy
They think it's all over, it is now!

Tinkley
1K Away
1K Away
Posts: 1495
Joined: Sat Jun 06, 2009 11:27 am
Location: N Hants England
x 6

Re: ABS fault. Help needed please!

Post by Tinkley » Tue Nov 24, 2015 2:59 pm

deltic wrote: Or could it be that non-ABS wheel bearing have been fitted? Is that possible? That said the ABS was working when I picked the car up and on one occasion after that... I did check around under the rear seat and nothing seemed amiss. I'll try to check around this coming weekend and report back.
Unlikely as I believe this 'first generation' ABS uses an actual rotor (small toothed gear), and magnetic coil to count the movement. Only second generation ABS systems require magnets in the wheel bearing with a Hall effect sensor. I may be wrong as I don't have an ABS equipped BX! but it would make sense as the early BMW bikes (with ABS) definitely had a toothed ring. The front hub parts are definitely ABS or non specific, most likely the rears are too, although the ring could be added to the back of the rear bearing housing.

User avatar
MULLEY
Over 2k
Posts: 8375
Joined: Thu Jun 22, 2006 11:10 pm
Location: Derbyshire
x 3

Re: ABS fault. Help needed please!

Post by MULLEY » Mon Nov 30, 2015 1:21 am

Will a pug 405 abs be suitable for the bx?
2002 C5 2.0 HDI Estate - Remapped - It goes better
2011 Mini Cooper D Clubman - it does over 60mpg
1992 TZD Turbo - SORN - slowly getting there
1991 Gti 16V - Blaze is back on the road since 2008
1990 Gti 8Valve SOLD - looks like it's been scrapped
2002 Mini Cooper S - SOLD - i miss this car
1992 TXD - Scrapped in March 2014

I'm not just a username, i'm also called Matthew.

User avatar
BOB6844
New Member
Posts: 11
Joined: Mon Sep 23, 2013 5:47 pm
Location: Up Holland, Lancashire

Re: ABS fault. Help needed please!

Post by BOB6844 » Mon Nov 30, 2015 9:24 pm

Have recently cured my offending ABS light by replacing two sensors. I was fortunate in acquiring a set of used spares from a frequent poster on this site. Hours were previously spent trawling for new replacements, including weeding out much mis-information from clowns advertising new goods they didn't have. The conclusion finally reached was that only original BX bits would suffice. Fortunately I was rescued at a very reasonable price.
My local Car Electrics expert tells me that ABS sensors are all different. This seems scarcely believable. The methods of fixing to the vehicle may well vary in detail, but the business end must surely be basically similar in vehicles of the BX's vintage. Has anyone done any serious investigation along these lines? Has anyone made contact with Juratek, UK manufacturers of "ABS Sensors and Extension Leads".
David

User avatar
MULLEY
Over 2k
Posts: 8375
Joined: Thu Jun 22, 2006 11:10 pm
Location: Derbyshire
x 3

Re: ABS fault. Help needed please!

Post by MULLEY » Tue Dec 01, 2015 11:58 pm

I thought most BX ABS issues were more to do with the wiring than the actual sensors themselves, but i must admit it would be bloody great to find somewhere where you could just get brand new one's as the illuminated ABS lamp is an MOT fail & personally i'd rather have working ABS. I know you can rewire the lamp to something else so that it goes out, but i'd rather have the safety feature working.
2002 C5 2.0 HDI Estate - Remapped - It goes better
2011 Mini Cooper D Clubman - it does over 60mpg
1992 TZD Turbo - SORN - slowly getting there
1991 Gti 16V - Blaze is back on the road since 2008
1990 Gti 8Valve SOLD - looks like it's been scrapped
2002 Mini Cooper S - SOLD - i miss this car
1992 TXD - Scrapped in March 2014

I'm not just a username, i'm also called Matthew.

User avatar
deltic
BXpert
BXpert
Posts: 607
Joined: Tue Jan 25, 2011 10:48 pm
x 9

Re: ABS fault. Help needed please!

Post by deltic » Wed Dec 02, 2015 9:17 pm

Well, I broke out the multimeter and tested all the sensors on the car and the spare. All read between 1020 and 1060 ohms apart from the offside rear which would appear to be the faulty sensor. If I'm feeling brave I'll investigate further this weekend.
1991 BX GTi Auto, grey, 133,000 miles (2015 & 2017 Citroen Classic Challenge veteran)
2006 C4 VTR+ 2.0 Coupé, silver, 60,000 miles

Kaapelimies
BXpert
BXpert
Posts: 206
Joined: Wed Feb 10, 2010 9:01 am
Location: Hollola, Finland
x 8

Re: ABS fault. Help needed please!

Post by Kaapelimies » Thu Dec 03, 2015 6:51 pm

I had a situation with ABS in my 4x4. I measured _everything_. Luckily there's a good documentation for the ABS and it's very simple to check everythign from the connector of the ABS ECU. All seemed to be OK. I have never heard of a broken ABS ECU, but now I have one. Luckily replacement part was bought with a burned 4x4 just a week before the problem arised :D .
BX 4x4 estate, several BX Van's and some more normal estates in Finland.