Anti-lock Brake light

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phaeton
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Anti-lock Brake light

Post by phaeton »

The anti-lock brake light has started to stay on on the 1995 Xantia SX Diesel. Has anybody any ideas where to start looking? Is there a unit to check or would it be best to start at each wheel & make sure the sensors are connected? Never had a problem before with the whole car in the last 8 years & 100k Cheers
miked
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Post by miked »

Try searching this forum for abs and flicker
When you turn the ignition on, does the warning light flicker at all before staying on? The light flickers while the control unit is checking the sensors, so if it doesn't flicker then it could be an indication that the control unit may be faulty. If it does flicker before staying on then it could indicate a faulty sensor.
samtronic
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Post by samtronic »

If the light turns on and stays on when you start the car before driving off, the connection to a sensor is bad.
If the light turns on while driving, the signal from a sensor is erratic. Others have reported weird brake behaviour when this happens.
This can be caused by intermittent connection or dirt on the sensor or sensor cogwheel.
The problem might be a bad connection in the connector, the wire to the sensor or the thin wire inside the sensor. The first two are relatively easy to fix, while the third requires either a new sensor (easiest way) or opening, unwinding, rewinding and sealing of the sensor.
You can check the sensors if you have a multimeter:
- Locate the ABS ECU (between the battery and the LHM reservoir)
- Disconnet the plug on top and measure the resistance between the following pins (Some of the pin numbers are moulded into the plug):
1 and 6: Right Front
15 and 30: Left Front
29 and 31: Right Rear
19 and 28: Left Rear
The resistance should be apx. 1050 Ohms (1.05 kOhms).
You can see some pictures here:
http://medlem.spray.se/xm94/XANTIA/fels_abs.html
(Translation tool here: http://www.systransoft.com/index.html)
You should also be able to find quite a bit of info regarding ABS sensors on this forum if you search it.
Søren
phaeton
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Post by phaeton »

Thanks guys, I did search before posting but only for 'anti-lock' which brought up no results, never thought about 'abs' Doh!!
Anyway in answer to your questions, the light comes on 'hard' when the ignition is switched on & stays on permanently. I'll put the multimeter round the pins & see what I get.
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Clogzz
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Post by Clogzz »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by phaeton</i>


The light comes on 'hard' when the ignition is switched on & stays on permanently.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Had that fault after rain.
Came good by itself.
mudinureye
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Post by mudinureye »

on my BX this atarted happening. It was due to the sensor.casing rubbing on the wheel. I now need a new sensor.
jeremy
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Post by jeremy »

Earlier Xantia ABS controllers are prone to failure but are repairable by specialists so long as the box hasn't been opened (safety reasons). Having said that the first step is to meter the sensors and ensure continuity. The light may also come on if there are other electrical faults like a blown fuse.
http://www.bba-reman.com/index.htm
http://www.carelect.demon.co.uk/
jeremy
phaeton
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Post by phaeton »

Right proved it's the offside sensor that is not working, how difficult are they to change? Selling the car next week so it would be good to do it before it goes.
phaeton
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Post by phaeton »

Ooops should have said offside REAR sensor
cmac51brae
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Post by cmac51brae »

xantia abs warning light stays on from start up. i have no abs , already tested ecu ,and is fine. can anyone help driving me mental
mkelly1
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Post by mkelly1 »

[quote]<i>Originally posted by samtronic</i>

If the light turns on and stays on when you start the car before driving off, the connection to a sensor is bad.
If the light turns on while driving, the signal from a sensor is erratic. Others have reported weird brake behaviour when this happens.
This can be caused by intermittent connection or dirt on the sensor or sensor cogwheel.
Søren
[/quote
Hi Soren,
Interested in what sort of "weird brake behaviour" people have had. My 1996 Xantia is troubling my workshop experts with intermittent low-speed "brake failure" - not quite ABS triggering, and not quite brake failure. As I roll to slow stop with gentle brake pressure, suddenly the pedal will go firm and brake effort decrease, almost like an engine stall. Occasionally, but not always, the ABS light will come on shortly after this happens. Is this the sort of weirdness a faulty sensor might cause?
With thanks,
Michael (Sydney Aus)
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Mandrake
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Post by Mandrake »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by mkelly1</i>

[quote]<i>Originally posted by samtronic</i>

If the light turns on and stays on when you start the car before driving off, the connection to a sensor is bad.
If the light turns on while driving, the signal from a sensor is erratic. Others have reported weird brake behaviour when this happens.
This can be caused by intermittent connection or dirt on the sensor or sensor cogwheel.
Søren
[/quote
Hi Soren,
Interested in what sort of "weird brake behaviour" people have had. My 1996 Xantia is troubling my workshop experts with intermittent low-speed "brake failure" - not quite ABS triggering, and not quite brake failure. As I roll to slow stop with gentle brake pressure, suddenly the pedal will go firm and brake effort decrease, almost like an engine stall. Occasionally, but not always, the ABS light will come on shortly after this happens. Is this the sort of weirdness a faulty sensor might cause?
With thanks,
Michael (Sydney Aus)
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Yes,
That sounds a lot like an intermitant wheel sensor - it could be either the sensor, or the cable connecting to the sensor.
My theory is that an intermitant connection on one sensor can momentarily cause the computer to think the car is going much faster than it really is (because the measured "speed" on the faulty sensor is much higher) with 3 locked wheels, (because the other three sensors are still reporting the true speed) causing it to release the brakes.
Normally ABS should not operate below approximately 20Km/hr, so if the ABS is releasing the brakes at very low speeds it either thinks the speed is higher than it really is, or the computer is flakey. (The latter being unlikely)
Finding out for sure WHICH sensor it is without a lot of trial an error could be tricky though. As with most intermitant faults, they never play up when you go looking for them [:D]
Try a search on this forum for a massive big thread on ABS problems similar to this...
Regards,
Simon
mkelly1
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Post by mkelly1 »

Thanks Simon. Very interesting theory. I guess in my case, this would have resulted in symptoms occurring at various speeds, not just at walking pace. Nevertheless, it gets me thinking about the algorithms used by the computer to make its logical triggering decisions. We would all hope that they are robust and well proven, but you never know!!
Cheers/Michael
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