ABS Fault Warning

Mandrake · Post by **Mandrake** » 18 Jun 2006, 23:04

Kowalski wrote:"Should" and "Could" are two entirely different words.

In theory, the ABS system should failsafe, in practice it doesn't always.

My point exactly. To quote a famous saying "In theory, theory and practice are the same, in practice they aren't"

I've had my ABS do slightly odd things when I had a dodgy cable on an ABS sensor. In my case, the ABS would occasionally cut in when it shouldn't BUT it only affected the circuit that had the dodgy sensor, i.e. the rest of the brakes worked properly BUT I did have to press the pedal harder.

I've had that happen as well as the complete half second failure of brakes at very low speed.

I have a theory that a flat accumulator sphere could cause problems in combination with the ABS, but I don't know how the ABS system interupts the brakes and whether it needs additional pressure to operate. Somebody who understands the mechanics of the ABS valve block could no doubt rule out or confirm this theory as plausable or not.

You are quite right about this - a flat accumulator sphere is highly likely to impact on the effective operation of ABS.

Since ABS works by releasing and re-applying the brakes several times a second, it does somewhat rely on the intantaneous stored pressure provided by the accumulator sphere.

The result could be the brakes being mostly released for a second or so until the pump cuts back in to bring the pressure up, rather than pulsing on and off rapidly. So when the ABS *did* trigger, it wouldn't work very effectively.

However with the problem being discussed the fact is the ABS should not be activating under any circumstances for light braking below the threshold speed. (Of approx 20Km/hr)

Regards,
Simon

AndersDK · Post by **AndersDK** » 18 Jun 2006, 23:04

Simon -

You had an event with a dodgy 500 ohm's sensor as failing - Amen to that.
Its definately not my problem if your ABS ECU did not detect that fault - I think you should address that to Citroen.

And why would I think that either a shortcircuit or open-circuit sensor detected by the ECU is saving he world against any other faults ?

I simply mention above that the ECU does that.

I dont believe - or try to convince - that there would be no other fault situations ?
Are you trying to put on me that the ABS ECU is not that smart it ought to be ?

Mandrake · Post by **Mandrake** » 18 Jun 2006, 23:08

Lets agree to disagree Anders....

I'm sure that if one day this strange and disconcerting problem happens to you you might change your mind.

Regards,
Simon

AndersDK · Post by **AndersDK** » 18 Jun 2006, 23:11

Mandrake wrote:Lets agree to disagree Anders....

I'm sure that if one day this strange and disconcerting problem happens to you you might change your mind.

Regards,
Simon

Change my mind from what sonny

stevenlizuk · Post by **stevenlizuk** » 19 Jun 2006, 09:50

What Have I started?,

This is clearly a subject which needs a definitive answer.

In conclusion, we know that a duff sensor can fool the ABS ECU into reacting stangely.

In my car at least if the sensor re-asserts itself during the journey the ECU turns the ABS on again.

My accumulator is fine and the LHM is within two years old and at the correct height.

It is however my opinion (not fact), that the ABS re-activates too easily in the face of overwhelming evidence of an intermittant fault (on and off again in the same journey) and that when it's all said and done the ECU is only as good as it's interpretation of what it's being told.

From this point on, if my ABS is ever giving me problems I will disconnect it straight away until it is fixed, rather than let the car decide for itself whether or not it feels like stopping when I do.

The point of the forum is surely to share the knowledge and experience of owning one of these somewhat eccentric cars, not to bicker about what can or cannnot happen under given circumstances.

When I know exactly what has happened to the car I will tell the forum and we can take it from there.

Thanks to all who have contributed.

Steve

p20 · Post by **p20** » 19 Jun 2006, 22:33

My ABS light has been coming on for awhile now, needs to be sorted for MOT next month.
About 2 months ago, the ABS kicked in at walking pace(after just being started). It turned out the rear caliper was leaking on the kerb side.
Drove it home very carefully, once the ABS light came on the dashboard, the brakes were ok, as the other three still worked as normal. Not ideal or to be recomended, but enough to crawl home. So in my case the ABS fault worked in my favour, briefly, but i would NOT recommend it