ABS Light on all the time

[skog77]

My Xantia is developing quite a personality.

Today when i fired up the car the ABS light was on and never went off. This has never happened before. To check i took it on a gravel road, and i'm pretty sure the ABS has stopped working. It's a 1995 2.0 8V Automatic.

First step was to check the fuses under the hood and the steering column, they are fine.

Next step was to measure the resistance (Ohm) to the individual ABS sensors.
(I'll put in the info here in case someone needs to know at some point.)

I removed the connector to the ABS unit (next to the fuses in the engine bay) and measured resistance. The pins are as follows:

Left Rear: 28-19
Right Rear: 29-31
Left Front: 15-30
Right Front: 1-6.

You should get about 1000-1100 ohms, mine were all about 1200 so they appear to be fine.

But the light is still on, and the ABS system is not working. I have MOT coming up soon...

Any ideas? Could there be a fuse that is not listed as part of the ABS system in the manual?

[spider]

There might be a fuse or two relays in the ABS module itself.

I'd get it on a Lexia really which will at least tell you *why* the light is on.

[skog77]

I love this forum, cause i get quick answers

I dont have a Lexia though. Can it actually give such specific answers?

[spider]

It should explain why the light is on the description might be confusing though but it will say why its on.

If you did want to guess it would take ages could be a broken wire between the unit and the multiplug on the sensor connector or even a faulty module itself.

A generic cheaper fault code reader *might* read ABS faults I'm not sure, I know they won't generally do Airbag SRS issues or immobiliser / key coding issues.

[VertVega]

If all the resistant readings are OK then you should next check the condition of the toothed rings.
Start checking the front ones which are easier to reach than the rear ones.
Check if they
- are fixed and not loose
- have any missing material

Did you read this thread in Handy Hints & Tips --> Xantia Rear ABS Sensor Renewal

[Mandrake]

If the light comes on with the key and never goes out it won't be the toothed rings - a fault with the toothed rings can only be detected when the car is in motion so the light would come on and go out as normal, but then come back on again a few seconds after driving off.

If its coming on with the key and never extinguishing then its one of only a few things:

* No power to the ABS ECU (The light is powered by default even if the ECU is unplugged, the ECU turns the light OFF when it's functional and happy)

* Faulty ECU

* Faulty static resistance reading to one of the sensors - which has already been checked and ruled out.

A further test that you could do would be to double check there is a good power and ground to the ECU as measured at the ECU connector. If that tests ok then you really have no choice but to get it tested on a Lexia otherwise you're just stabbing in the dark.

[skog77]

Late reply here, but yeah it was the ECU that was broken, confirmed by my friends newly aquired Lexia.

Fix: Remove the ABS warning light bulb from the dashboard.

MOT passed no problem!

[citroenxm]

ABS ECU's that are attached to the Hydraulic block ARE changable WITHOUT removing the ABS Block.

Remove the battery.. Slacken the Fuse box mount bolts and move it forward slightly.. Theres 2x T25 (or 30) Torx screws in the front, and a clip at the bottom, feel for it, release the clip and the ECU will come away forwards.

New one can be fitted. Its a common thing, the Tevis ECUs do give up, as you have found.

[Old-Guy]

Late reply here, but yeah it was the ECU that was broken, confirmed by my friends newly aquired Lexia.

Fix: Remove the ABS warning light bulb from the dashboard.

MOT passed no problem!

MoT tester not paying attention - all warning lights must light when 'ignition' is switched on (to test that no bulbs have been removed) - should have been a fail.

Never mind, 12 months to fix the fault!