Abs Repair.

The ABS on the estate packed up about six months ago, but as the MOT is rapidly approaching, I thought I had better do something about it.

Most of the necessary information is available elsewhere on the forum, but I thought I would bring it together into a practical application. My information only applies to sensor faults as that is the most common problem

The first thing you need to do is acertain which sensor/s are not working, this is quite simple using an ohm meter and the following information.

Remove the plug from the ABS ECU, on the opposite end to where the cable goes in see four pairs of staggered contacts, these are connected as follows:

The pair nearest the end (pins 18 & 35) are connected to the N/S/Front,
The next (pins 17 & 34) O/S/Rear
The next (pins 16 & 33) O/S/Front
The nearest (pins 15 & 32) N/S/Rear

You should get a reading across all these pairs of about 2500 - 2600 Ohms, if one or more read much in excess of this, typically 3 or 4 meg ohms, that's where the problem lies. In all probability the sensor will be OK, the usual problem is a poor connection at the connector to the loom.

Mine showed two open circuit, both the o/s ones. The front one is quite easy to get at, jack up the appropriate side and remove the wheel, follow the lead from the sensor and you will find it goes to a two pin plug/socket at the lower end of the inner wing. Seperate the plug/socket, check for 2500 oohms across the pins, if OK give the pins a scrape with a thin screwdriver until they are shiny, apply a little grease and plug the lead and check the appropriate plug pins again.

The rear ones are not quite so easy as the connectors are on top of the subframe, it will be necessary to drop the subframe one side. This is not as difficult as it sounds. Jack up and remove the wheel again then put a jack under the subframe of the wheel you have removed, jack up to take the weight. Slacken the bolts in the opposite end of the subframe by two or three turns, do not remove them, remove completely the subframe bolts at the end you are working on and lower the jack sufficiently to be able to reach the connector. If it is the nearside rear you are doing, be careful not to lower the subframe to much as it will press on the filler hose to the tank and make it leak, if you do, jack it up a little and it should stop. It will only lower just enough to get your hand in on the n/s rear. Put something between the subframe and chassis so the gap cant close up if it should fall of the jack or something or it could be nasty. Give the plug socket the same treatment as the front and check at the plug again.

Having done all this, I checked the plug again and found that the front o/s had gone o/c again on further examination I found that the lead from the plug was o/c where it goes into the plug, the problem now is how to make a watertight join. I cut off the lead at the plug, after removing the rubber sealant, cleaned the tags with a thin sharp screwdriver and soldered the replacement lead onto them, any flexible two core mains cable will do. I then sealed the join with silicone rubber. The other end, which I cut just below the bracket that also holds the brake wear warning lead, leaving about 2" of wire for the connection. I found a length of rubber tube that would slide over comfortably over the lead, about 3" will suffice, I then seperated and stripped the ends of the wires, 1/2" of bare wire is sufficient, soldered one pair with a length of sleeving slid over it, and then the other pair. For good measure I coated the join with waxoil, I then slid the rubber tubing over the joint and fitted a cable tie at each end, should make a good waterproof joint and it looks quite good too

I now have a fully functioning ABS system it goes for MOT on tuesday....

Peter.N.

This post has been edited by Peter.N. on July 24, 2008 05:52 pm

Peter,

I found you dont have to lower the subframe, but I guess you could if you want to attach the sensor back on its fixing point

Nice information, I wonder if thats whats wrong with my girl, the light is on and off all the time, and even on WITH functioning ABS...

Good info...

Rgds
Paul

Hi Paul

I wanted to make it as simple as possible - I dont bend as easily as I used to

If your Abs is working I would think that all the sensors must be in tact.

Peter

Hi Peter & Paul

My guess is that the rubber cable sheath ages and starts to crack across the cross-section because it is bent to a curve and oscillates when the vehicle is moving. The two stranded copper cores will still hold good and there will be no ABS problems. Then the individual copper strands will fracture one by one but even with one complete set of wire strands gone the remaining rubber of the sheath and the remaining wire may well keep the broken copper ends together enough to pass current particularly when the vehicle is static. In this state it will probably pass the initial ABS start up test and put the light out most of the time.

Often thought about trying cable replacement on ABS sensors. Pleased, Peter that you have shown than it can be done successfully.

Regards

John

Hi John

That is excactly what mine had been doing, light went out when I started up and then came on when I moved off, although of late it had been staying on all the time, probably due to the failure of the rear connection.

Twin round plastic mainslead is similar in diameter to the original and it all went quite well ...for the present.

Peter.

Peter-you can get something called 'heatshrink sleeving' you slide an appropriate length on the cable BEFORE you solder-insulate the 2 cores-slide the sleeving over and heat ( a hairdryer is normally sufficient) and it shrinks down quite tightly. it comes in differing sizes/colours and is obtainable form most electrical wholesalers.

Alan.

Hi Alan

Uesd lots of the stuff before I retired as a TV engineer but didn't have any of the right diameter and I am certainly not going to buy any more - I'm trying to get rid of my stock! The piece of fuel line I used was a very neat fit and I am sure will be watertight, I only sleeved one lead to keep the diameter down, its still working a treat - but, the ABS has packed up on the other one now!

Thanks anyway

Peter.

OOps! I do think that XM are organic with a mind of their own! Incidentally-Citroen XM and I sorted out a problem-that you'd highlighted-on my hard suspension-even though it'd had the e-crofting diode fix it looked as if certainly 1and maybe 2 of the mosfets were showing signs of frying. A replacement ECU restored comfort! The offending ECU put away for future repairs if needed!
Also a spray with switch cleaner seemed to sort out an intermittent ABS problem too.

Alan.

Scraping both pins from the front connectors made the light go out and car passed MOT.
Info was a great help. . Thanks Peter.

This post has been edited by lemoenman on September 18, 2008 09:40 pm

Guys!

You should also check the distance between the sensor and the ABS ring.
If You are so unfortunate as me, to have Bendix breaks on Your XM´s, clean the sensor, ABS ring and adjust the distance on the little screw on the sensor.
The gab must only be 0,5mm!

I have chanced all 4 sensors and the cost was huge. Around 1.000 £ !?

Bad luck Soren, they can be had for about £65 each here, I thought that was expensive enough.

Derek

This post has been edited by DerekW on September 19, 2008 06:03 pm

Yes Derek....

That is very bad luck. Many things are expensive i DK. The most stupid thing to learn afterwords is, that i could have bought at unoriginal sensor to about 18£ and modify it, so that it fits

Are you sure, that 65£ is the price for a Bendix sensor and not a Teves?

In DK a Teves sensor cost about 73£ each

You were too late in retrofitting the diodes. The MOSFETS were already doomed as the original diodes had already failed. You might want to install the E-Crofting package to prevent another ECU fry as the MOSFET failure is likely due to an electro valve diode foul. Your call.

This post has been edited by Jan-hendrik on September 20, 2008 02:57 pm

You're right Soren, it was a Teves that I bought at that price. Egg on face time again.

Derek

65 quid, 73 quid? Uhh, at this threshold, no big difference, me thinks