Abs Warning Light Question

[94xm]

Hi,

My first post here, i have a series one, 94 xm auto 2.1 td estate.
Just reconnected the computer screen and put a bulb in the abs warning light in the dash, and suprise suprise the abs is not clearing with abs out of use. Disconnected by the previous owner....

Now the light does a tiny flicker twice before going off for a little while longer then coming on and staying on. A total guess but is the tiny series of flickers some sort of order of checking the wheels sensors and if so which one is shot or the wiring broken too?

Thanks for any help

Mark

[noz]

Hi Mark,

Welcome to club-xm. I hope you find it friendly and helpful. For future reference it may be useful to put the year and model of your car in your signature so that the next time you ask a question everyone knows to which model it refers. Just click on 'My Controls' at the top right, 'edit my signature' at the bottom left of the next screen and then fill in the white box in the middle of the next.

ABS is one of the most common faults with the XM. 99% of the time its the sensors which are to blame or more correctly the cables leading out to each sensor. Citroen in their wisdom put the joint in the cable in the most inhospitable location on the car and then failed to provide any protection for them. The easy test is to pop the bonnet and locate the ecu for the ABS. If you have a Bendix system then its very easy. It should be located in the black plastic box on the offside(right) inner wing. There will be more than one ecu in there but the one you're looking for has only one connector, its black and its held on at one side by a spring clip and at the other end by a plastic hook. Lift the ecu out of its box and locate the spring clip. Bend it out of the way and the big plastic wiring plug should pop free at one end. Continue to lift the plug and the hook will come free at the other end. (To refit just locat the hook at one end and press the plug home until the spring clip snaps back into place)

Look at the brown connectors on the underside of the plug with the big cable to your right. At the end opposite to the cable end you'll find a cluster of 8 connectors grouped together in two rows. Starting from the left the pairs are grouped vertically. The first pair is terminals 35 and 18 and these are for the front left wheel
The second pair is terminals 34 and 17 and these are for the rear right wheel
The third pair is terminals 33 and 16 and these are for the front right wheel
The first pair is terminals 32 and 15 and these are for the rear left wheel

A measurement taken across each pair should read approx 2000ohms. There should also be no reading between any of the pins and any good earth point on the car.

Although its possible that it may be something else it is the easiest thing to check and works 99% of the time.

If you find you have a Teves ABS system then the ecu is below the battery tray bolted to the side of the ABS block. I've never worked on one so I cant tell you which order the pins are in on the plug. However, here are the pins and to which wheel they refer:
Pins 15 and 30 Left Hand Front
Pins 1 and 6 Right Hand Fornt
Pins 28 and 19 Left Hand Rear
Pins 29 and 31 Right Hand Rear

Hope that helps. Please let us know how you get on.

Cheers

noz

[xmexclusive]

Hi Mark

The ABS does a power on test on startup, during this it puts the light on and off. Unfortunately this enables a MOT tester to spot (and fail) cars where the ABS is defective and the fault bulb has been removed. This is not unique to XM's.
The quickest way to find out what is wrong is to get it fault read using one of the Citroen devices. Citroen Dealers usually charge for this and are not usually free with the results or willing to be watched. Try to find an independant with the kit or perhaps the odd club member may be able to help.
If the test device cannot see your ABS then it has lost its 12 volt supply or a fuse has blown. Typically the ABS has feeds from F1, F5 & F23 in the passenger side fuse box. If the device can test then you will get the faulty components identified.
You will have a Bendix ABS system fitted. This has a hydraulic block in the engine compartment down just behind the bottom of the radiator on the passenger side. There is also a relay on the hydraulic block. This supplies 12 volts when the system is in working order or else earths it. There are 2 or 3 electrical connectors to the hydraulic block and it is worth checking that the connections are not corroded. There is an ABS ECU in the Black Box to the drivers side of the engine. It is normally the one furthest back, black not silver with a single large connector and will be marked Bendix. Again it may be worth unplugging and remaking the connections (corrosion here would be unusual on the contacts). Later on if all else fails you can check the resistance of each of the ABS sensors from this plug (pin pairs are usually 15/32 16/33 17/34 18/35). Sorry cannot remember the resistance value but no doubt someone else will help with this. There are connectors on each of the cables to the ABS wheel sensors. Corrosion is often a problem with these connectors. The rear two are on the top of the rear suspension arms and a real sod to get at but the front two are in the back of the front wheel arch and easy to check. I suspect Citroen dealers regularly change wheel sensors when cleaning the connection will solve the problem for a while.
I have found with ABS faults that it is worth cleaning up the actual sensors and the toothed wheels as the first step then check the fuses and the connectors you can get at easily. Then if not solved move on to either the professional system check or the sensor resistances. Not everybody agrees with me about the value of cleaning the sensors and toothed wheels but it is easy to do and brakes generate a lot of very fine metallic dust that mixed with muck and grease I believe can alter the magnetic field the sensors see.

Sorry for the length of the response particularly if I have cover items you already know about. Hope it helps.

Regards

XMexc

[94xm]

Excellent,

Thanks Noz for the info, im glad there are people who know these things inside out. This is the 2nd i have had the first identical, but 197000 on the clock when the lower pulley failed shooting a peice of rubber in between the cam belt, jamming it. Real shame! It was an auto too, and drove perfect.

Anyway back to this one. Great info , i will let you know how i get on.

Incidently where are the connections to the abs sensors, i assume on the rear arms or front struts? I read your removal procedure, sounds like a nightmare! hope its the cabling.
I want another 100k out of this one!

Cheers

Mark

[94xm]

Another fast reply ,many thanks XMexc.

I will go through that info and see how i go.
Many thanks to the both of you.
Great Forum!

cheers

Mark