I have also had my brakes fail at low speed on my xantia HDI 110 then restore just before I got to the handbrake.Unlike others I did not get an ABS light come on. After reading the previous reports
I checked my front sensors and found the left hand one was not fitted
correctly, leaving it with a large air gap and not square to the tooth ring on the drive shaft.After reseating the sensor to give the 0.5mm air gap my brakes have returned to normal.This was all due to a servicing error on my part during a drive boot change.Other information I found from the french revue techique xantia manual;
sensor resistance 1,000 to 1,400 ohms, L/Hand front sensor pins 1-2,
RHF 19-20,LHR 5-6,RHR 22-23 on ECU. I hope this helps others.
---------------------------------------------------------------
2000 Xantia HDI SX 34k
1990 BX TZS 120k
1989 BX TRS 250k
Xantia ABS Fright
Moderator: RichardW
Wow, scary stuff 
After reading this entire thread, and having some understanding of electronics and sensors etc, I think I can possibly see what is going on here in most of the cases.
The key seems to be faulty sensor data coupled with the 10Kph cutoff limit.
The only way the ABS computer would know what the vehicle speed was, would be from the wheel sensors themselves. The sensors just generate a pulse every time one of the teeth on the driveshaft joint passes under the sensor, and the computer counts the number of pulses per second to work out the speed of that wheel, based on knowing how many teeth there are in 360 degrees, and the approximate wheel diameter.
Some of the causes people have found are a build up of muck in the teeth, incorrect sensor positioning (too far away from the teeth) and intermitant wires going to the sensor.
All three of these problems (but especially the second and third ones) could easily cause erroneous additional pulses per second to get sent to the ABS computer and make it think that the car is going faster than the 10Kph limit below which the ABS should shut off.
Meanwhile the other wheel sensors are registering lower speeds, and the computer may think those wheels are locking.
I'll take a punt here, and guess that the ABS computer assumes that the *fastest* speed reading of the four wheels is the speed that the car is actually going, and that it assumes if all 3 other wheels register a much lower speed they must all be locking up, and it starts doing its ABS thing.
Now the problem is clear - you're coasting to a stop and doing maybe 3Kph, but one of your sensor wires is broken and the engine vibration is vibrating it such that the wire is rapidly contacting and breaking - suddenly the ABS computer thinks that wheel is doing 25Kph while the other 3 wheels are doing 3Kph - panic stations ! It will slam into full ABS action and remove nearly all braking.
Under normal wheel locking conditions as soon as it removes the braking from a wheel the speed of the wheel will suddenly jump back up to a similar speed to the non-locking wheels as the tire grips and the wheel spins up again. When this happens, the ABS unit will apply some braking to this wheel again, etc.
But under these abnormal conditions it removes the braking from the wheels that are only doing 3Kph, and they still continue to do 3Kph instead of speeding up so it doesn't reapply the brakes again !! It assumes they're still locked and keeps waiting!
Only two things will cause it to reapply the brakes at this point:
a) the faulty sensor connection comes right, probably due to vibration etc.
b) the faulty sensor stops sending pulses to the ABS computer altogether, in which case the ABS computer probably has a 1 second timeout before deciding that the sensor is faulty, and ignoring it. (And thus reapplying the brakes)
(a) would cause no ABS fault light to appear, (because the problem went away without the ABS computer realising there was a problem) while (b) would cause an ABS fault light to appear just after the brakes started working again, as it realised the sensor was dead, and started to ignore it.
How does this theory fit in with peoples experiences ?
If I'm right, the moral of the story is CHECK YOUR SENSORS CAREFULLY. Make sure theres no muck around the teeth, make sure the alignment of the sensor is carefully set, and check for frayed or damaged wiring to the sensor. If you've already experienced these problems, don't take chances with the wiring to the sensor - replace it...
When I get a car with ABS I'll definately be giving the sensors a once over after reading this thread
Regards,
Simon
After reading this entire thread, and having some understanding of electronics and sensors etc, I think I can possibly see what is going on here in most of the cases.
The key seems to be faulty sensor data coupled with the 10Kph cutoff limit.
The only way the ABS computer would know what the vehicle speed was, would be from the wheel sensors themselves. The sensors just generate a pulse every time one of the teeth on the driveshaft joint passes under the sensor, and the computer counts the number of pulses per second to work out the speed of that wheel, based on knowing how many teeth there are in 360 degrees, and the approximate wheel diameter.
Some of the causes people have found are a build up of muck in the teeth, incorrect sensor positioning (too far away from the teeth) and intermitant wires going to the sensor.
All three of these problems (but especially the second and third ones) could easily cause erroneous additional pulses per second to get sent to the ABS computer and make it think that the car is going faster than the 10Kph limit below which the ABS should shut off.
Meanwhile the other wheel sensors are registering lower speeds, and the computer may think those wheels are locking.
I'll take a punt here, and guess that the ABS computer assumes that the *fastest* speed reading of the four wheels is the speed that the car is actually going, and that it assumes if all 3 other wheels register a much lower speed they must all be locking up, and it starts doing its ABS thing.
Now the problem is clear - you're coasting to a stop and doing maybe 3Kph, but one of your sensor wires is broken and the engine vibration is vibrating it such that the wire is rapidly contacting and breaking - suddenly the ABS computer thinks that wheel is doing 25Kph while the other 3 wheels are doing 3Kph - panic stations ! It will slam into full ABS action and remove nearly all braking.
Under normal wheel locking conditions as soon as it removes the braking from a wheel the speed of the wheel will suddenly jump back up to a similar speed to the non-locking wheels as the tire grips and the wheel spins up again. When this happens, the ABS unit will apply some braking to this wheel again, etc.
But under these abnormal conditions it removes the braking from the wheels that are only doing 3Kph, and they still continue to do 3Kph instead of speeding up so it doesn't reapply the brakes again !! It assumes they're still locked and keeps waiting!
Only two things will cause it to reapply the brakes at this point:
a) the faulty sensor connection comes right, probably due to vibration etc.
b) the faulty sensor stops sending pulses to the ABS computer altogether, in which case the ABS computer probably has a 1 second timeout before deciding that the sensor is faulty, and ignoring it. (And thus reapplying the brakes)
(a) would cause no ABS fault light to appear, (because the problem went away without the ABS computer realising there was a problem) while (b) would cause an ABS fault light to appear just after the brakes started working again, as it realised the sensor was dead, and started to ignore it.
How does this theory fit in with peoples experiences ?
If I'm right, the moral of the story is CHECK YOUR SENSORS CAREFULLY. Make sure theres no muck around the teeth, make sure the alignment of the sensor is carefully set, and check for frayed or damaged wiring to the sensor. If you've already experienced these problems, don't take chances with the wiring to the sensor - replace it...
When I get a car with ABS I'll definately be giving the sensors a once over after reading this thread
Regards,
Simon
-
goldfinche
- Posts: 128
- Joined: 08 Jan 2005, 02:29
- Location: United Kingdom
- My Cars:
Hi first of all may I apologise for going a little off topic.I dont bother with Xantia stuff because I havnt got one,yet.My son has a BX with ABS and finds that without ABS the brakes are the usual very effective responsive BX brakes.The ABS light comes on and the brakes are in his words "crap" they give the impression that the car is not going to stop.This has been narrowed down to a intermitant front sensor, insidently I was sitting in the car and was pressing the brake pedal for bleeding the brakes(LHM change.)was a bit too quick and had the pedal pressed before the nipple was openned and the pedal kicked back so hard that it shot my foot off the pedal.
So can see a small link here,Light on bad brakes sensor fault pedal kick back.
Not trying to confuse matters but just a thought.
There was a report on Xantia ECU failures caused by a voltage problem, over voltage IIRC or an over voltage spike. this was in a section of faults by a ECU repair firm that I found a long time ago (a year or so) I think they were German or perhaps Dutch, Sorry I cant be more spacific but lost everything when the computor destroyed its hard drive.
Cheers.
Geoff
So can see a small link here,Light on bad brakes sensor fault pedal kick back.
Not trying to confuse matters but just a thought.
There was a report on Xantia ECU failures caused by a voltage problem, over voltage IIRC or an over voltage spike. this was in a section of faults by a ECU repair firm that I found a long time ago (a year or so) I think they were German or perhaps Dutch, Sorry I cant be more spacific but lost everything when the computor destroyed its hard drive.
Cheers.
Geoff
Il thow my spanner in now... [:D]. On my old bx, there was in intermittant abs problem, and it did just what everyone on here is saying, at slow speeds, the car was more or less without brakes, until suddenly, bam, and you bang your head on the windscreen. Quite scary. Problem on this car was the handbrake was poor (needed adjusting) and in incidents around the works yard, it lost both bumpers and required replacements. However, when the abs light was on, the brakes were fine. Strange fact was that it passed 3 MoT's in this state. The car was however scrapped before anything could be done, so I dont really know where the problem was. My advice at this point would be, stay away from ABS...
However, on the bx I had previous to that without the ABS, I ran into the back of someone on the M1 when I first got it, all because the brakes were so damned good, and on the astra I had before hand, they were so damned crap! (so in this case abs would have saved me a pair of new bumpers....).
So, my revised advice would be to have ABS, and maintain it.
However, on the bx I had previous to that without the ABS, I ran into the back of someone on the M1 when I first got it, all because the brakes were so damned good, and on the astra I had before hand, they were so damned crap! (so in this case abs would have saved me a pair of new bumpers....).
So, my revised advice would be to have ABS, and maintain it.
When I purchased my BX estate in 1999 it had superb brakes - with no pads, knackered discs and no ABS. It still has superb brakes with ABS and good discs and pads. I suppose I'm aware of the ABS working about 15 times during the whole time I've had it unless deliberately provoked and at least a couple of the times it has operated I've wondered if it was a help or not.
Jeremy
Jeremy
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Peter.N.
- Moderating Team
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C5 X7 VTR + Satnav Hdi estate Silver
C5 X7 VTR + Hdi Estate 2008 Red
In the past: 3, CX td Safaris and about 7, XM td estates. Lovely cars. - x 1207
As far as I am concerned ABS is an unnecessary complication, just something else to go wrong. I managed to stop allright for about 40 years before we had it, in fact I have had more scares with ABS operating, making the car feel as though it will not stop, than I ever did without it. I agree, it does reduce stopping distance under some circumstances, but if people drive like lunatics (present company excepted) they will crash into things whatever saftey features the car has. I would disconnect mine, but it wouldn't pass the MOT.
-
Kowalski
- Posts: 2557
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- My Cars: Ex 05 C5 2.0 HDI Exclusive 145k
Ex 97 Xantia 1.9TD SX 144k
Ex 94 Xantia Dimension 1.9TD 199k
ABS does give you the impression that you have an infinite amount of brakes available to you, since they never lock the wheels. It also makes the car feel unstable when you're braking on the limit.
With ABS you can end up with all the wheels intermittently locked which can make the car feel like its sliding about a bit, where as if you were non-ABS you'd only be locking the fronts and having to release them, the car would feel more stable but its giving less braking.
With ABS you can end up with all the wheels intermittently locked which can make the car feel like its sliding about a bit, where as if you were non-ABS you'd only be locking the fronts and having to release them, the car would feel more stable but its giving less braking.
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by fastandfurryous</i>
Unfortunately the effect of ABS, ESP, EBA, TCS, and in fact, airbags, good brakes etc etc. in many cases has simply been that people drive faster and use up any benefit the systems have given. <b>All over the world it has been shown that despite massive advances in car safety technology, the number of people being killed on the roads refuses to go down.</b>
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
I was browsing for ABS faults in this thread, and found your interesting post. Actually, the gloomy situation with road fatalities isn't uniform across the world. Australia has, I gather, a rather more restrictive and more effectively policed traffic system than some parts of the world. When I got my licence about 30 years ago, the road toll in NSW alone was about 1100 pa. It has steadily fallen to about 520, while the number of vehicles and annual vehicle-kilometres have dramatically increased. Fatalities per vehicle pa are now about one-tenth of a generation ago. Vehicles and roads have both improved, so it <u>can </u>be done if drivers accept that their poor habits will be curbed.
Cheers/Michael
Unfortunately the effect of ABS, ESP, EBA, TCS, and in fact, airbags, good brakes etc etc. in many cases has simply been that people drive faster and use up any benefit the systems have given. <b>All over the world it has been shown that despite massive advances in car safety technology, the number of people being killed on the roads refuses to go down.</b>
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
I was browsing for ABS faults in this thread, and found your interesting post. Actually, the gloomy situation with road fatalities isn't uniform across the world. Australia has, I gather, a rather more restrictive and more effectively policed traffic system than some parts of the world. When I got my licence about 30 years ago, the road toll in NSW alone was about 1100 pa. It has steadily fallen to about 520, while the number of vehicles and annual vehicle-kilometres have dramatically increased. Fatalities per vehicle pa are now about one-tenth of a generation ago. Vehicles and roads have both improved, so it <u>can </u>be done if drivers accept that their poor habits will be curbed.
Cheers/Michael