I assumed (wrongly) that all ABS systems would use a Hall effect sensor and not just some, therefore appologies to you Phil[:I]
But what ever type, they are there for the very same purpose and both generate a pulsing signal from the proximity of a moving ferrous object.
On another note, I've seen it written several times that during ABS operation, if the pedal is pumped by the driver this can actually result in confusing the ECU, so the advice is that if the worst comes to the worst, keep the pedal planted until the danger is over or you KYAG, don't try to influence the situation via the pedal yourself as this increases the risk of having to KYAG.
Dave
Xantia ABS Fright
Moderator: RichardW
I think the worrying part about this fault, theories apart, is that this can and does happen, it is frightening and dangerous when it does. I have had ABS for many years now on various cars mainly Hondas, and have never experienced this type of fault,or any fault associated with the ABS. in fact there has only been a very, very few times that the ABS has operated, mainly when I have forced it just to confirm that it is working. This Xantia that I own is my first and I have had it for about 11 months and overall am very impressed with it, but I think I would rather it did not have ABS, who knows when it will strike again. The point that I was trying to make previously about Garages was that I think quite often they will make a guess as to what is wrong rather than spend the time testing if they are only being asked for advice, there is a previous thread on this forum were the poster had a ABS fault, he took it to the garage who said it was the ECU, he bought a secondhand ECU for £100.00, took the car back to the garage to have it fitted and it turned out that the fault was in fact a front wheel sensor, he sold the ECU on Ebay and got most of his money back.
-
DoubleChevron
- Posts: 622
- Joined: 22 Sep 2003, 18:06
- Location: Australia
- My Cars:
- Contact:
Hi Guys,
I bet the poeple that have experiance 'temporary brake failures' have all done so at very low speeds ??
I think what happens is it waits for continuous signals from all other wheels before deciding one sensor is dud. If your going very slowly, it'll take longer to make that desision as the gear is passing the sensor a lot slower. Maybe the ECU waits for a full turn or 2 of any sensor before deciding the ABS isn't working correctly.
either way I had this happen in my CXturbo 1week after I got it. What happened was I backed up a drive and nearly took someones car out. I hit the anchors and nothing happened [:0][:0] being a CX turbo there is next to no engine braking, also being a CX the handbrake isn't worth a pinch of sh!t. The brakes came good (after about 2seconds) just as I was about to hit something !!!!!!
Certainly scared the sh!t out of me, even if I was only going to hit at slightly higher than walking pace.
The up side, my ABS has been working intermittantly ever since (oneday I will find time to look at it), and this has never happened again...
seeya,
Shane L.
I bet the poeple that have experiance 'temporary brake failures' have all done so at very low speeds ??
I think what happens is it waits for continuous signals from all other wheels before deciding one sensor is dud. If your going very slowly, it'll take longer to make that desision as the gear is passing the sensor a lot slower. Maybe the ECU waits for a full turn or 2 of any sensor before deciding the ABS isn't working correctly.
either way I had this happen in my CXturbo 1week after I got it. What happened was I backed up a drive and nearly took someones car out. I hit the anchors and nothing happened [:0][:0] being a CX turbo there is next to no engine braking, also being a CX the handbrake isn't worth a pinch of sh!t. The brakes came good (after about 2seconds) just as I was about to hit something !!!!!!
Certainly scared the sh!t out of me, even if I was only going to hit at slightly higher than walking pace.
The up side, my ABS has been working intermittantly ever since (oneday I will find time to look at it), and this has never happened again...
seeya,
Shane L.
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by DoubleChevron</i>
Hi Guys,
I bet the poeple that have experiance 'temporary brake failures' have all done so at very low speeds ??
seeya,
Shane L.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Nope; about 50/60 kph in my instance and with Mark, he was approaching the roundabout so again I would suggest no there either.
We are all aware of the under 10KPH syndrome and this isn't it.
I think the thing that is so frustrating from the point of view of us who have suffered it is that it is so hard to describe & even harder to prove.[V]
Alan S
Hi Guys,
I bet the poeple that have experiance 'temporary brake failures' have all done so at very low speeds ??
seeya,
Shane L.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Nope; about 50/60 kph in my instance and with Mark, he was approaching the roundabout so again I would suggest no there either.
We are all aware of the under 10KPH syndrome and this isn't it.
I think the thing that is so frustrating from the point of view of us who have suffered it is that it is so hard to describe & even harder to prove.[V]
Alan S
-
uhn113x
- Posts: 1161
- Joined: 06 Jan 2004, 22:06
- Location: Near Leeds, United Kingdom
- My Cars: 1981 Dyane - on road all year round.
1982 GSA Pallas - on road April - September.
1997 ZX 1.9D Dimension. - x 1
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Well Mike - are'nt they all used to pick up a magnetic field
- can't argue against the different constructions and function methods - but my reference to these all designated as HallEffect sensors - is common by mechanics.
Logic you may say - as they all have the same basic function : to provide a sensor signal by inductive means.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
No problem, Anders - I was in electronics in a previous life, and tend to be pedantic first thing in the morning - it wears off as the day goes on......[;)]
I am glad mechanics call them such - I am wary of the species, anyhow.
- can't argue against the different constructions and function methods - but my reference to these all designated as HallEffect sensors - is common by mechanics.
Logic you may say - as they all have the same basic function : to provide a sensor signal by inductive means.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
No problem, Anders - I was in electronics in a previous life, and tend to be pedantic first thing in the morning - it wears off as the day goes on......[;)]
I am glad mechanics call them such - I am wary of the species, anyhow.
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by acrowot</i>
My car was travelling very slowly when my problem occured, Mark said" Pulling up at the first junction behind a couple of other cars, braking gently from a slow speed the ABS warning light came on"I have asked him what he meant by slowly but as yet no replly.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
.............but, under 10kph??????
Alan S
My car was travelling very slowly when my problem occured, Mark said" Pulling up at the first junction behind a couple of other cars, braking gently from a slow speed the ABS warning light came on"I have asked him what he meant by slowly but as yet no replly.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
.............but, under 10kph??????
Alan S
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David Goddard
- Posts: 138
- Joined: 26 Sep 2001, 04:39
- Location: United Kingdom
- My Cars:
My experience of three (!) ABS sensor failures:-
1) Inductive pick going open circuit - ABS light comes on instantly and stays on until the sensor is changed.
2) On both occasions they have gone open circuit within 5 secs of starting the car. Ignition on, ABS light on, ABS light off, then back on is what I have seen. It's clear that as part of the self test sequence, the ABS ECU must send a voltage to each coil to check they are present (checks for 1,000 ohm resistance). I think this test voltage can "burn out" the very thin copper wire.
3) Low output from a sensor will trigger the ABS warning light. However the light generally will not come on until after the car has been parked for some time. Apart from a pole piece being too far away from the toothed wheel (mechanical damage form a stone say), the usual reason for a low output is a dirty connector. Un-plug, clean with switch cleaner and reassemble with a smear of vaseline.
1) Inductive pick going open circuit - ABS light comes on instantly and stays on until the sensor is changed.
2) On both occasions they have gone open circuit within 5 secs of starting the car. Ignition on, ABS light on, ABS light off, then back on is what I have seen. It's clear that as part of the self test sequence, the ABS ECU must send a voltage to each coil to check they are present (checks for 1,000 ohm resistance). I think this test voltage can "burn out" the very thin copper wire.
3) Low output from a sensor will trigger the ABS warning light. However the light generally will not come on until after the car has been parked for some time. Apart from a pole piece being too far away from the toothed wheel (mechanical damage form a stone say), the usual reason for a low output is a dirty connector. Un-plug, clean with switch cleaner and reassemble with a smear of vaseline.
Alans
In my cases,there was more than one instance of this brake failure my car was always travelling under 10kph it used to take place just before I stopped, in one instance I was doing a 3 point turn and when braking on the first turn the brakes failed and my front wheels hit the kerb ( when I say hit more like touched the kerb as the car was only just moving ) on the other occasions the car was travelling in a straight line and and just before braking to a final stop the pedal seemed to sink further to the floor and there was no braking effect, for tunately braking restored before impacting car that had stopped in front of me. At these sort of speeds the ABS should not be functioning anyway (under 10kph) so logic seemed to tell me it was the ECU, which in my case was the case. As far as Mark,s speed I have only quoted what he said, only he knows what speed he was doing and I await his answer.
In my cases,there was more than one instance of this brake failure my car was always travelling under 10kph it used to take place just before I stopped, in one instance I was doing a 3 point turn and when braking on the first turn the brakes failed and my front wheels hit the kerb ( when I say hit more like touched the kerb as the car was only just moving ) on the other occasions the car was travelling in a straight line and and just before braking to a final stop the pedal seemed to sink further to the floor and there was no braking effect, for tunately braking restored before impacting car that had stopped in front of me. At these sort of speeds the ABS should not be functioning anyway (under 10kph) so logic seemed to tell me it was the ECU, which in my case was the case. As far as Mark,s speed I have only quoted what he said, only he knows what speed he was doing and I await his answer.
acrowot,
I'm not disputing the problem you had nor the fact that at under 10kph there's every possibility that there was something badly amiss when nothing worked, but in my case it was way above this critical 10kph and I suspect reading Mark's account that his was too.
It's just that I know what I'd done prior to this incident in my case as I had been having a fiddle with this faulty sensor and managed to get it to work...I thought (incorrectly) and as Mark mentioned his sensor problem also, I would have to have serious doubts that all of a sudden and coincidentally, he has an ECU failure and all these diagnosis based on just one malfunction. I didn't and I can see no reason that he should.
The distance travelled when brakes fail is greatly magnified due to the little tricks the mind plays on you. As someone who was involved for years in motor sport I've had it happen often and it definitely brings the mind back to the reality of the distance a car travels per second when it happens. As a result of my competitive experience, I'm not one inclined towards taking unnecssary risks when driving so I'm not being gung-ho about this.
Alan S
I'm not disputing the problem you had nor the fact that at under 10kph there's every possibility that there was something badly amiss when nothing worked, but in my case it was way above this critical 10kph and I suspect reading Mark's account that his was too.
It's just that I know what I'd done prior to this incident in my case as I had been having a fiddle with this faulty sensor and managed to get it to work...I thought (incorrectly) and as Mark mentioned his sensor problem also, I would have to have serious doubts that all of a sudden and coincidentally, he has an ECU failure and all these diagnosis based on just one malfunction. I didn't and I can see no reason that he should.
The distance travelled when brakes fail is greatly magnified due to the little tricks the mind plays on you. As someone who was involved for years in motor sport I've had it happen often and it definitely brings the mind back to the reality of the distance a car travels per second when it happens. As a result of my competitive experience, I'm not one inclined towards taking unnecssary risks when driving so I'm not being gung-ho about this.
Alan S
The ABS warning light on my 2.1 XM has also been playing up. Occasionally the ABS lamp will not extinguish and the matrix panel displays "ABS system out of action". If I then switch off and re-start engine everything is fine. However when the warning light has illuminated the brakes have always worked with the usual great efficiency. The only pattern I have been able to observe is that the last few times the light has come on, the car was being started on cold and damp mornings and after I drove through a large puddle. There was one time where the lamp came on when I switched on the air-con but it only did it once.
Reading mark SP's problem with his ABS makes me think that air has got into the system. I understand that whenever the hydraulics are depressurised for sphere replacement, the brakes should always be bled. Perhaps the garage that replaced the accumulator never did this?
I am still amazed how many people out there (though NOT on this forum) think ABS would help them stop when driving 6 feet from the car in front. It is one of those systems one is glad to have yet hope is never needed. (bit like an airbag) ABS helps you steer and brake at the same time (assuming the tyres have sufficient grip!) but is pretty much useless in snow and ice. On the Audi 80 there was a switch where you could lock-out the ABS when driving on snow.
Reading mark SP's problem with his ABS makes me think that air has got into the system. I understand that whenever the hydraulics are depressurised for sphere replacement, the brakes should always be bled. Perhaps the garage that replaced the accumulator never did this?
I am still amazed how many people out there (though NOT on this forum) think ABS would help them stop when driving 6 feet from the car in front. It is one of those systems one is glad to have yet hope is never needed. (bit like an airbag) ABS helps you steer and brake at the same time (assuming the tyres have sufficient grip!) but is pretty much useless in snow and ice. On the Audi 80 there was a switch where you could lock-out the ABS when driving on snow.
I downloaded this a while ago from Yahoo C5-L forum ...
*******************************************************
> Greetings to all.
> I will first describe my unpleasant experience with my C5, then
> describe the subsequent enquiries I made, than will ask specific
> questions in the hope that I can get more information.
>
> I have a C5 SX 1.8 litre automatic, model year 2002.
>
> On 7 May 2003 my wife was driving, me sitting next to her. Traffic was
> medium heavy. We were behind a truck, driving around 60 kph. The truck
> slowed and stopped at a red light. My wife braked, slowed, then when
> the car got to a slow speed, around 5 kph, it continued without
> slowing down further and did not stop. When the car was still far from
> the truck, about 10 meters behind the truck, I noticed what was
> happening and looked at my wife's foot. It was pushing hard on the
> brake, and only on the brake. The car continued traveling very slowly
> until it tucked its nose under the truck ahead. No damage to the
> truck, but the geometry of the truck was such that it caused an
> amazing amount of damage to the front of the car. I checked the road.
> It was dry and the weather quite dry.
>
> I have known the people in the dealer's service station for years and
> get good and professional service. They checked the brakes, and said
> there is no brake problem. They asked the country management and were
> told they have never heard of such a situation. They told me she must
> have had her foot on the gas and the brake together. I saw what
> happened. Her foot was on the brake only. I subsequently did an
> experiment where I kept my foot on the gas, then put the other foot on
> the brake. The car stopped.
>
> From a kind person in this discussion group I was led to an Internet
> group in German language that deals only with brake problems of the
> C5. I looked at their discussion with the help of a friend who
> understands German. I found there several entries of people with a
> similar problem. They report a very infrequent intermittent problem of
> insufficient braking force. I emphasise, very infrequent (for example
> in one entry, the report says 3 or 4 times in 25000 km) and
> intermittent. In every case the service people checked the brakes
> afterward and said everything was OK.
>
> It is disconcerting and difficult to drive with the feeling that the
> brakes are unreliable. This incident ended with me losing only money
> for my insurance deductible and the no-claim bonus. But what if we had
> been approaching a pedestrian crossing? We could have appeared
> culpable for injuring or killing someone. All I want is for Citroen to
> take responsibility and replace what is needed so that my car becomes
> reliable and the problem does not recur. I am not specially interested
> in making a big fuss.
>
> Now my questions. Has anyone experienced a similar problem? If so, how
> did you fix it?
Hmm, never heard of anything like this, might it be related to the
brake problems experienced by Volkswagen in their latest Passat ?
Both C5 and Passat are equipped with the same latest generation ABS
brakes from a German company named Bosch ...... Passat is known to
loose its brakes under certain conditions.
Luckily the handbrake of the C5 operates on the front wheels, so in a
tight situation it's safe to stop the car using the handbrake
On the other hand, it's an automatic and the automatic gearbox should
take a break when the brakes are fully applied, so it might be a
question of a software error in the automatic gearbox.
Or was the rubber/textile mat rolled up beneath the pedal, preventing
it from being fully pressed down ? That would for sure cause the
phenomena, because the automatic gearbox would never get the signal
from the brakes that it should go into neutral state.
*******************************************************
So, strange things happen, aren't they ?
*******************************************************
> Greetings to all.
> I will first describe my unpleasant experience with my C5, then
> describe the subsequent enquiries I made, than will ask specific
> questions in the hope that I can get more information.
>
> I have a C5 SX 1.8 litre automatic, model year 2002.
>
> On 7 May 2003 my wife was driving, me sitting next to her. Traffic was
> medium heavy. We were behind a truck, driving around 60 kph. The truck
> slowed and stopped at a red light. My wife braked, slowed, then when
> the car got to a slow speed, around 5 kph, it continued without
> slowing down further and did not stop. When the car was still far from
> the truck, about 10 meters behind the truck, I noticed what was
> happening and looked at my wife's foot. It was pushing hard on the
> brake, and only on the brake. The car continued traveling very slowly
> until it tucked its nose under the truck ahead. No damage to the
> truck, but the geometry of the truck was such that it caused an
> amazing amount of damage to the front of the car. I checked the road.
> It was dry and the weather quite dry.
>
> I have known the people in the dealer's service station for years and
> get good and professional service. They checked the brakes, and said
> there is no brake problem. They asked the country management and were
> told they have never heard of such a situation. They told me she must
> have had her foot on the gas and the brake together. I saw what
> happened. Her foot was on the brake only. I subsequently did an
> experiment where I kept my foot on the gas, then put the other foot on
> the brake. The car stopped.
>
> From a kind person in this discussion group I was led to an Internet
> group in German language that deals only with brake problems of the
> C5. I looked at their discussion with the help of a friend who
> understands German. I found there several entries of people with a
> similar problem. They report a very infrequent intermittent problem of
> insufficient braking force. I emphasise, very infrequent (for example
> in one entry, the report says 3 or 4 times in 25000 km) and
> intermittent. In every case the service people checked the brakes
> afterward and said everything was OK.
>
> It is disconcerting and difficult to drive with the feeling that the
> brakes are unreliable. This incident ended with me losing only money
> for my insurance deductible and the no-claim bonus. But what if we had
> been approaching a pedestrian crossing? We could have appeared
> culpable for injuring or killing someone. All I want is for Citroen to
> take responsibility and replace what is needed so that my car becomes
> reliable and the problem does not recur. I am not specially interested
> in making a big fuss.
>
> Now my questions. Has anyone experienced a similar problem? If so, how
> did you fix it?
Hmm, never heard of anything like this, might it be related to the
brake problems experienced by Volkswagen in their latest Passat ?
Both C5 and Passat are equipped with the same latest generation ABS
brakes from a German company named Bosch ...... Passat is known to
loose its brakes under certain conditions.
Luckily the handbrake of the C5 operates on the front wheels, so in a
tight situation it's safe to stop the car using the handbrake
On the other hand, it's an automatic and the automatic gearbox should
take a break when the brakes are fully applied, so it might be a
question of a software error in the automatic gearbox.
Or was the rubber/textile mat rolled up beneath the pedal, preventing
it from being fully pressed down ? That would for sure cause the
phenomena, because the automatic gearbox would never get the signal
from the brakes that it should go into neutral state.
*******************************************************
So, strange things happen, aren't they ?
You would almost have to think that at low speeds it either has to be that the ECU "switches off" or the explanation of air in the system is worthy of thought. But, how do you get air into a sealed from the factory system?
As another theory, if one wheel sensor at above the 10KPH were to have a short/fault that told the ECU that a wheel was locking, (ie) send a signal showing the wheel not rotating; would that not cause the other 3 to not operate?
I'm open for suggestions on this because as we've seen; whilst in theory it's claimed to be impossible, we are seeing more examples from cars where it has occurred and I am still to be convinced in my case & possibly Mark's that the sensor isn't at the root cause.
Alan S
As another theory, if one wheel sensor at above the 10KPH were to have a short/fault that told the ECU that a wheel was locking, (ie) send a signal showing the wheel not rotating; would that not cause the other 3 to not operate?
I'm open for suggestions on this because as we've seen; whilst in theory it's claimed to be impossible, we are seeing more examples from cars where it has occurred and I am still to be convinced in my case & possibly Mark's that the sensor isn't at the root cause.
Alan S