ABS - My Nemesis

[Ross]

Here we go again - the car is a Xantai VSX 1.9TD manual with an ABS faul that "appeared" one night (actually the day before the prebooked MOT).
The dashboard light was constantly on when the ignition was on and/or the engine running - best advice on forum and web was a ecu fault so the ABS ecu was checked repaired and guaranteed ok.
The fault persisted and the Citroen Dealer tested the system and advised the fault was with the fr offside sensor - just fitted the sensor and the fault persists

Does the ecu require resetting at any stage ?
Anyone any suggetions as all I have left is giving it to the main dealer to sort (and find loads of money no doubt to pay him)

Thanks
All

[Mandrake]

Hi Ross,

Looks like the "best advice" wasn't so good.... rarely are the ABS ECU's faulty, its usually a sensor/wire fault.

My suggestion if you have an always on light would be to unplug the big plug from the ECU and use a digital ohm meter to measure each sensor AT the ECU plug. (There could be a fault in the wiring loom between the big ECU plug and the individual plugs to the sensors)

If you search hard enough on the forum you'll find the pinouts for the plug. (I know they're here somewhere - as I used them to diagnose mine, although I can't find it with a quick search..)

They should be around 1000 ohms, and all within about 100 ohms of each other. If the ABS light comes on and stays on as soon as you start the car before you even drive off, its a simple continuity fault. (open, shorted, or too far away from 1000 ohms)

If it comes on after you're moving its either a problem with the sensor not picking up adequate signal from the teeth on the hub (alignment, sensor, dirt in the teeth etc) or an intermitant wire flexing with suspension travel or vibration.

And no, I don't know of any "resetting" required for an ABS ECU - you can reset the fault counters with the diagnostic computer, but they don't have any bearing on whether the ABS light comes on as far as I know.

When the fault goes away the light should be out the next time the ignition is turned on, so a solid light indicates the fault still exists...

Regards,
Simon

[Homer]

Hi Ross,

Looks like the "best advice" wasn't so good.... rarely are the ABS ECU's faulty, its usually a sensor/wire fault.

The early (pre 1995 IIRC) ones were prone to failure but I would have thought they would all have failed and been replaced by now.

[windysurferuk]

Have a look at this post

http://www.frenchcarforum.co.uk/forum/v ... highlight=

It contains the diagrams and required pin numbers

cheers

[Gammy leg]

Ross

If the light stays on regardless of whether the car is moving or not it is probably not related to the wheel sensors. Check out the ABS pump relay pins for corrosion, this will give symptoms that you have. I would guess that it is situated under front N/S wheel arch.

Gammy

[Mandrake]

Hi Gammy,

When my front right sensor cable was faulty the ABS light was on all the time except for a brief flash during the self test when the key was first turned on....

ABS pump relay ? I think you'll find that Xantia ABS systems don't need an ABS pump

(It just needs a hydraulic control block thanks to the high pressure hydraulic system already in the system...)

Regards,
Simon

[deian]

So cool when people get the simplest things wrong about the way a xantia works, "no no, ours doesn't have that" or "on our it's like this", even i need to think twice sometimes, simple mistake though!

[Ross]

The ABS may be a problem - but its worth having a Citroen just to use this forum - thanks all - deep breath and star again

[PowerLee]

Check the instrument panel earths too, If one of these is lose the ABS light will come on

Found that out with my old 405, Lose earth connection = Intermittent ABS warning light coming on.

Also will do the same if both brake light bulbs are blown, Brake light switch is faulty or if both rear lamp clusters are unplugged.