Thanks for the link jeremy, that could be very useful. I assume the pinouts described in that document are different on the Xantia, this post would certainly suggest so:
http://www.andyspares.com/discussionfor ... hTerms=abs
I think you could well be on to something regarding the brake light switch not turning the system on, but I'm unsure how I can test it really. The brake lights work.
I need to call in at the dealer tomorrow to collect some disc retaining screws for doing the brakes, I may ask nicely if they could copy the relevant section from the Xantia manual for the ABS for me.
Xantia ABS
Moderator: RichardW
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Homer
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<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by alexx</i>
Homer, I still don't have a Xantia (didn't find a proper one yet), but on several Xantias I've driven, pulsing on the pedal during ABS in action was like in other cars, just a little less intensive. You can't miss it.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
I've had a '94 version and now have a '98 estate and like I said, the only times I have noticed any pulsing has been with one wheel on mud. And believe me, I have needed the ABS more times than I like to recall. I wouldn't buy a car without it now.
Homer, I still don't have a Xantia (didn't find a proper one yet), but on several Xantias I've driven, pulsing on the pedal during ABS in action was like in other cars, just a little less intensive. You can't miss it.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
I've had a '94 version and now have a '98 estate and like I said, the only times I have noticed any pulsing has been with one wheel on mud. And believe me, I have needed the ABS more times than I like to recall. I wouldn't buy a car without it now.
Well, it's hard to oppose to someone, who has been driving Xantia for quite a time, like you. But I'm also quite sure I felt pulsing upon activating the ABS, although not nearly so nasty like in other cars.
Brake valve is constructed in a fashion that it resists to the brake pedal with the force proportional to the 'output' pressure. There is a hole in both slide valves (for front and rear brakes), leading the 'output' pressure to the bottom side of the valve, opposite to the brake pedal - it's done that way. Since ABS valves are varying this output pressure, this should be felt at the pedal also.
What about other Xantia owners - can you feel the pulsing on the pedal when you activate the ABS or not?
Brake valve is constructed in a fashion that it resists to the brake pedal with the force proportional to the 'output' pressure. There is a hole in both slide valves (for front and rear brakes), leading the 'output' pressure to the bottom side of the valve, opposite to the brake pedal - it's done that way. Since ABS valves are varying this output pressure, this should be felt at the pedal also.
What about other Xantia owners - can you feel the pulsing on the pedal when you activate the ABS or not?
I don't think you need to know the pinout no to check the continuity of the brake light switch circuit. If you remove the plug from the ICU and simply connect one side of a meter to the brake light switch with 2 connectors (or 2 wires in one) and try all the pins in the plug. One should conduct, 2 or none - you've got problems.
Silly thought - you've got working brake lights haven't you? - had switch fall apart on holiday last year!
jeremy
Silly thought - you've got working brake lights haven't you? - had switch fall apart on holiday last year!
jeremy
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blueboy2001
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Yes I have got working brake lights.
I had a chat with one of the mechanics at the dealers on Wednesday and he got the wiring diagrams out. He said the brake pedal switch is not involved with the ABS, although there is a connection shown on the diagram.
He offered to hook it up to the Elit machine one afternoon when they're not busy if I call in and see what that shows up - they are on a bit of charm offensive with me at the moment as I'm looking to swap 6 Citroen vans for the company I work for and they know I normally buy them from another dealer - he also said he would find an ABS relay for me to try if I wanted to. His thoughts were either the relay or a bad earth from the ECU.
I will clean up the earth plate on the car and then arrange to borrow a spare relay and see if that corrects it.
I had a chat with one of the mechanics at the dealers on Wednesday and he got the wiring diagrams out. He said the brake pedal switch is not involved with the ABS, although there is a connection shown on the diagram.
He offered to hook it up to the Elit machine one afternoon when they're not busy if I call in and see what that shows up - they are on a bit of charm offensive with me at the moment as I'm looking to swap 6 Citroen vans for the company I work for and they know I normally buy them from another dealer - he also said he would find an ABS relay for me to try if I wanted to. His thoughts were either the relay or a bad earth from the ECU.
I will clean up the earth plate on the car and then arrange to borrow a spare relay and see if that corrects it.
I have read this topic with interest as I have a similiar ABS light problem although mine only stays on if the car has been standing a while ie in the morning it will stay on after ignition, but once I arrive at work and switch off if I was then to switch back on the abs light goes out and it stays out and actually works, which is odd as it sort of tells me that it is not a itermittant connection as it is to regular a coincidence , however after what I have read here I will go home tonight and check all the sensors out from the ECU connector, but just wondered if any one else has had this variant before? The lamp does flicker before going out aswell
Xantia TD running on 50/50 vegetable oil what fuel tax??
Xantia TD running on 50/50 vegetable oil what fuel tax??
Weirder still went home last night eager to test the sensors. The light Wwas on all the way home switched off came back with me meter and switched on light went off , so I thought theres not much point trying to check the wiring if all is ok so I went out in it , rocked the steering slapped the relays banged the fuses still stayed off! came back in an hour light still went off so I THOUGHT GREAT IT'S FIXED 
left it there undisturbed through the night got up this morning turned the key and the light stayed on! any ideas as to what's making this happen? seems like it's taking the P out of me 
left it there undisturbed through the night got up this morning turned the key and the light stayed on! any ideas as to what's making this happen? seems like it's taking the P out of me Wolfie,
In my experience the front wheel sensors are the most likely thing to give an annoying intermittant fault. So many Xantias have needed them replacing yet broadly speaking the rest of the system is quite reliable. It is true some ECUs fault but I'd always look at that last after checking everything else. Be wary of reading too much into the pattern of failure (ie light operation) such that you say it can't be the wheel sensors. Bear in mind the ECU checks the wheel sensor resistance first at rest, and then when rolling at a few mph it checks for the correct output signal....a faulty cable can give some confusing symptoms.
Blueboy,
To double check that your warning lamp hasn't been fiddled with...
Remove the ABS fuse and the lamp should stay on all the time with the ign. Then replace the fuse and unplug the green ABS relay (under the cover near the ECU). This should mean the ABS lamp never lights at all. Note: Whenever making/removing ABS connections have the ign off.
I've known folks go to huge lengths to try and get the warning lamp out completely when just pulling the green relay will do it in seconds!
By the way pressures of work in other Citroen related fields have kept me away from here since the forum re-started back earlier in the year. It's one of the best Citroen forums and I'll try to pop in more now...if only to learn from Dave Burns!!
David
In my experience the front wheel sensors are the most likely thing to give an annoying intermittant fault. So many Xantias have needed them replacing yet broadly speaking the rest of the system is quite reliable. It is true some ECUs fault but I'd always look at that last after checking everything else. Be wary of reading too much into the pattern of failure (ie light operation) such that you say it can't be the wheel sensors. Bear in mind the ECU checks the wheel sensor resistance first at rest, and then when rolling at a few mph it checks for the correct output signal....a faulty cable can give some confusing symptoms.
Blueboy,
To double check that your warning lamp hasn't been fiddled with...
Remove the ABS fuse and the lamp should stay on all the time with the ign. Then replace the fuse and unplug the green ABS relay (under the cover near the ECU). This should mean the ABS lamp never lights at all. Note: Whenever making/removing ABS connections have the ign off.
I've known folks go to huge lengths to try and get the warning lamp out completely when just pulling the green relay will do it in seconds!
By the way pressures of work in other Citroen related fields have kept me away from here since the forum re-started back earlier in the year. It's one of the best Citroen forums and I'll try to pop in more now...if only to learn from Dave Burns!!
David
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blueboy2001
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Interesting:
ABS Fuse (F1 in Engine Bay box) - Light operates as normal
ABS Relay Unplugged - Light operates as normal
ABS ECU Multiplug Uplugged - Light remains on permanently
I'm not even going to attempt to work out how they've rigged that up. The previous owner had a habit of "creative" repairs using household items. The best (worst) on I've come across is the windscreen wiper linkage pivot point which had worn through and had been repaired using what appeared to womens knicker elastic!
ABS Fuse (F1 in Engine Bay box) - Light operates as normal
ABS Relay Unplugged - Light operates as normal
ABS ECU Multiplug Uplugged - Light remains on permanently
I'm not even going to attempt to work out how they've rigged that up. The previous owner had a habit of "creative" repairs using household items. The best (worst) on I've come across is the windscreen wiper linkage pivot point which had worn through and had been repaired using what appeared to womens knicker elastic!
Woolfie
I had much the same problem. When I got the car it turned out 3 ABS sensor leads had failed and I repaired them with multicore co-ax cable carefully soldered. I had had no trouble with the back ones but one of the front ones had failed again as I didn't get a good cable run. When this went it was intermittent (and seemingly weather dependant!) and when I got the same problem again this year immediately thought it was the same one.
However with great restarint I metered them before doing anything else and found it was a back one. so I cut the wire to see if the fault was in the old wire (which was ropey) and ended up back at the sensor which itself seems to have failed. It has now been replaced with a new one (very tight fit) and all is lovely.
The point of this tale is that they do fail intermittently and I suggest that when the light won't go out you test them all for continuity.
As D.J.Woollard says suspect the ECU last - however tempting it is to blame a complicated black box!
jeremy
I had much the same problem. When I got the car it turned out 3 ABS sensor leads had failed and I repaired them with multicore co-ax cable carefully soldered. I had had no trouble with the back ones but one of the front ones had failed again as I didn't get a good cable run. When this went it was intermittent (and seemingly weather dependant!) and when I got the same problem again this year immediately thought it was the same one.
However with great restarint I metered them before doing anything else and found it was a back one. so I cut the wire to see if the fault was in the old wire (which was ropey) and ended up back at the sensor which itself seems to have failed. It has now been replaced with a new one (very tight fit) and all is lovely.
The point of this tale is that they do fail intermittently and I suggest that when the light won't go out you test them all for continuity.
As D.J.Woollard says suspect the ECU last - however tempting it is to blame a complicated black box!
jeremy
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RichardW
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Blueboy
Well, I had a good look at the wiring diagram for the BX ABS (not exactly the same, but very similar) last night in Haynes. It’s far from simple!
There are in fact FOUR power supplies to the ABS ECU:
1. Brake light switch – power supply tells ECU brake is pressed (well, brake light switch is closed and live anyway!)
2. ‘Primary’ supply – fed from the ignition switch – no separate ABS fuse
3. Light supply. Light is fed +ve from the ignition switch, and earths via the computer
4. ‘Main’ supply – this comes via the ABS fuse and relay (wired in series).
Primary and main are my descriptors to make this description easier
There is no internal circuit diagram, so this is what I think should happen….
Ignition on – unit is powered up via the primary supply and begins self test, and test of sensors etc. ABS light is lit by virtue of the ECU allowing it to earth.
Self / sensor check passed – the unit powers up the relay switching circuit and checks to see that it is receiving the ‘main’ supply. If so it switches out the earth from the light to put it out (or more likely supplies 12V to the earth side so there is no voltage across the lamp).
Rolling test – this is continuous – if the ECU decides that it is receiving false / bad information from the sensors it will power down the relay and relight the warning lamp.
There is a slight complication here – in its un-powered state the relay appears to connect the computer to an earth. I am not sure if this is where the warning light earths or not – I don’t think so, as this would not allow the unit to check it was receiving ‘main’ power before putting the light out – but I do not know without a functional description or internal circuit diagram.
Now, to my mind this should result in the following lamp operation scenarios:
Fuse out – lamp permanently on.
Relay out – lamp permanently on (although if it does earth through the relay, then the lamp will be permanently off!)
Multiplug out – lamp permanently off – there is no earth for the lamp with the plug disconnected, so it should not light.
This does not tie in with your observations at all, so either:
1. I am wrong in the above and / or the Xantia system operates very differently to the BX one.
2. There has been some jiggery-pokery in your system!
I prefer 2……
Maybe you can ‘find a friend’ with (working) ABS so you can swap the computers over and see what happens to yours with a known good computer connected – I DOUBT it would damage another computer, but you can never be sure!!
The ECU in my mate's TD went belly up - light on all the time. A replacement from a breakers yard cured it, and the system now works OK.
Does this help? Who knows.....
Richard W
Well, I had a good look at the wiring diagram for the BX ABS (not exactly the same, but very similar) last night in Haynes. It’s far from simple!
There are in fact FOUR power supplies to the ABS ECU:
1. Brake light switch – power supply tells ECU brake is pressed (well, brake light switch is closed and live anyway!)
2. ‘Primary’ supply – fed from the ignition switch – no separate ABS fuse
3. Light supply. Light is fed +ve from the ignition switch, and earths via the computer
4. ‘Main’ supply – this comes via the ABS fuse and relay (wired in series).
Primary and main are my descriptors to make this description easier
There is no internal circuit diagram, so this is what I think should happen….
Ignition on – unit is powered up via the primary supply and begins self test, and test of sensors etc. ABS light is lit by virtue of the ECU allowing it to earth.
Self / sensor check passed – the unit powers up the relay switching circuit and checks to see that it is receiving the ‘main’ supply. If so it switches out the earth from the light to put it out (or more likely supplies 12V to the earth side so there is no voltage across the lamp).
Rolling test – this is continuous – if the ECU decides that it is receiving false / bad information from the sensors it will power down the relay and relight the warning lamp.
There is a slight complication here – in its un-powered state the relay appears to connect the computer to an earth. I am not sure if this is where the warning light earths or not – I don’t think so, as this would not allow the unit to check it was receiving ‘main’ power before putting the light out – but I do not know without a functional description or internal circuit diagram.
Now, to my mind this should result in the following lamp operation scenarios:
Fuse out – lamp permanently on.
Relay out – lamp permanently on (although if it does earth through the relay, then the lamp will be permanently off!)
Multiplug out – lamp permanently off – there is no earth for the lamp with the plug disconnected, so it should not light.
This does not tie in with your observations at all, so either:
1. I am wrong in the above and / or the Xantia system operates very differently to the BX one.
2. There has been some jiggery-pokery in your system!
I prefer 2……
Maybe you can ‘find a friend’ with (working) ABS so you can swap the computers over and see what happens to yours with a known good computer connected – I DOUBT it would damage another computer, but you can never be sure!!
The ECU in my mate's TD went belly up - light on all the time. A replacement from a breakers yard cured it, and the system now works OK.
Does this help? Who knows.....
Richard W
we appear to have got 2 threads going here so here's my bit to confuse everyone!
Wolfie - i was thinking that the experts willtell you that you need an oscilloscope to check the function of your sensors while they are operating. An alternative is to listen to them. I have used this method sucessfully at one stage and all I did was to connect the output straight from a sensor to the amplifier input on a radio an drive round listening to the drone and for snap crackle and pops. If you are lucky 3 will sound the same and one will be different!
I was fortunate in having a radio with a 5 pin din input direct into the amplifier stage. I would have thought that any cassette recorder would do although you might have to listen to a recording if you couldn't persuade it to 'monitor'
Incidentally bumps sound most dramatic but that appears normal. Its breaks and crackles you are listening for.
jeremy
Wolfie - i was thinking that the experts willtell you that you need an oscilloscope to check the function of your sensors while they are operating. An alternative is to listen to them. I have used this method sucessfully at one stage and all I did was to connect the output straight from a sensor to the amplifier input on a radio an drive round listening to the drone and for snap crackle and pops. If you are lucky 3 will sound the same and one will be different!
I was fortunate in having a radio with a 5 pin din input direct into the amplifier stage. I would have thought that any cassette recorder would do although you might have to listen to a recording if you couldn't persuade it to 'monitor'
Incidentally bumps sound most dramatic but that appears normal. Its breaks and crackles you are listening for.
jeremy
Richard,
Pressure of "actual" Citroen work as opposed to "virtual" advice prevented me looking at the ABS book wiring info last night. However I can say that the Xantia system is different to the BX and that the warning lamp should stay on if you disconnect the ECU.
As far as I'm aware unplugging the green relay is the only way to disable the warning lamp full time. Odd that something so simple will work when they've gone to so much trouble to stop fiddling the light out other ways.
As soon as I have a day spare I intend to write up the Xantia ABS diagnostic procedure for the Citroen Car Club, I'll make it available here as well.
David
Pressure of "actual" Citroen work as opposed to "virtual" advice prevented me looking at the ABS book wiring info last night. However I can say that the Xantia system is different to the BX and that the warning lamp should stay on if you disconnect the ECU.
As far as I'm aware unplugging the green relay is the only way to disable the warning lamp full time. Odd that something so simple will work when they've gone to so much trouble to stop fiddling the light out other ways.
As soon as I have a day spare I intend to write up the Xantia ABS diagnostic procedure for the Citroen Car Club, I'll make it available here as well.
David