Another new Xantia Owner

[nick19800]

Hi nick

Watch the blink sequence on the ABS light.
This tells you if and at what stage the ABS is failing the start-up checks.
There should be 3 blinks followed by another 3 blinks.
Fault finding in an ABS can waste a considerable amount of time and money if you do not find out which system is fitted then apply the tests for that particular system. I think early Xantias are Teves Mk4 fitted.
The ECU's are pretty bomb proof but there is more than one power feed. Loss of any one will fail the start-up test.
For start-up the power feeds and relay are checked, the 2 microproccessors in the ECU then the resistance of the 4 wheel sensors. That set of checks is then repeated hence the second set of 3 blinks.
Sensor signals are not checked until the vehicle is on the move above a set speed with no brake application. So you do not have to worry about the fault being sensor signals or ABS rings until the start-up test is working and the ABS light comes on irregularly while on the move.

John

I had a look this morning and when it's starting the abs light is just on and stays on with no flashing at all.

[xmexclusive]

Hi Nick

That means that the the ECU is not getting as far as completing the start-up test. It is failing when it is testing out the ECU power supplies and components so no point in chasing the sensors yet.
Lexia most likely will not see the ECU in this state so would be no help.
Check the fuses and power feeds to the ECU. Clean the contacts on the ECU plug. After that check the ABS relay operation and the diode that seperates the ECU from the ABS warning light.
Once these are working the system should blink twice as it goes through the start-up test. If the light then stays on it is time to do the static resistance test to determine sensor faults. These are just as likely to be poor connections as actual sensor failures.

John

[CitroJim]

Is there any way of checking with a multimeter

Yes, have a look at this thread....

The Lexia is the diagnostic tool and will do the same job for the ABS as a multimeter as described in Kev's thread, only quicker...

The cruise control is a known troublesome area and often just a duff vacuum pump or duff brake switch. Both are easy to rectify...

This thread will give you a comprehensive cruise fault-finding guide.

As far as I know there is no connection between the ABS and the Cruise but if the vehicle speed sensor was duff the cruise would not work and maybe the ABS neither. If your speedo is working then the speed sensor is OK.

Electric windows: breaks in the wiring within the door concertinas is a very common issue on late Xantias.

If you need circuits of the windows, just ask... Ditto the full ABS circuit.

[nick19800]

Excellent, Now I have something to go by as I've not had much experience with citroens, I had a look at the plug which goes into the abs ecu and the contacts are very clean, Is there any way of checking the abs ECU?

[CitroJim]

Is there any way of checking the abs ECU?

Only with a Lexia. A few of us have them and in the Supersticky area there's a list of those that have them and where they are located...

If the multimeter tests draw a blank then that's your best bet. ABS ECUs are generally reliable though...

Note that the resistance measurements of the sensors are very critical. and if much above 1,100 ohms they can be considered duff..

[PhilGreaves]

Hi nick.

We have a mark 1 xantia which sufffered the same ABS symptoms and problems...repeatedly..just one of those things. But im guessing the following will be true for your later car too.

Around 10 years ago we were told by the garage it may need a new ECU. But when we asked around at the Citroen Car Club rally nobody had had to replace their ECU, at worst one person had a few dry joints that had to be resoldered. So good news is i wouldnt have thought your ecu needed replacement.

In the end we had the system tested manually. This revealed that the front nearside sensor was faulty. Replacing this cured the problem...for 5-8 years anyway.

Then last year we switched garages and our new mechanic* wouldnt pass the car for its mot. The orange abs dashboard light was on permanently from ignition and had been like this for about 3 years so we were shocked when he said that it wasnt a poor connetion and in fact we had no abs at all. dangerous and of course it meant it shouldnt have passed its mots. Moreover he says there is a simple way to check if your abs is working....

You can tell if your xantia has functioning abs by looking for a small red L.E.D behind a grill above the radio (i think its in the same place on mark 2s) it should be below some air vents. Anyway if the red L.E.D is flashing then you dont have abs (red meaning danger/warning etc). To fix this he replaced...once again the front nearside abs sensor.

However 2 days afterwards the orange abs light came on again from ignition (flickering) but the red L.E.D didnt (and still hasnt 8 months on). Our mechanic said that the flickering and now solid orange abs light on the dashboard was the result of a poor conection (makes sense as it goes out sometimes if you hit a bump).

So i would advise you to check the red L.E.D before pulling the car apart!

If the red L.E.D isnt flashing then as far as im aware you still have functioning abs. The orange light being on is only the result of a poor connection or some other fault.

If the red L.E.D is on then i would check the nearside front sensor first- it seems to be most likely to fail on these. (just be grateful you didnt buy a mk1 C5 they do have *real* electrical probelms...)

Hope that helps,
Phil

P.S the red L.E.D you are looking for is the one behind/within a grill not the smaller one on the radio panel...

* not a commercial advert etc but credit were credit is due the mechanic who told us about the red L.E.D thing was Graham Morton of GM Vehicle Services, holmbridge. Clearly a very intelligent mechanic.

[citronut]

Phill
if you mean the little red lamp in the centre of the interior air temprature sensor grill to the left of the time clock, this is the alarm warning lamp and i have never before heard it linked to an ABS fault/warnning,

i think your mechanic has got it wrong,


regards malcolm

[CitroJim]

I must admit, this is a new one on me... And I've been all over Xantia ABS like a rash, right from the earliest sinkers to the later MK2s.

[PhilGreaves]

Yes i do. I actually think its just a very well kept secret.

I do think our mechanic is correct but am prepared to stand corrected!

Right now the orange abs light is on yet the L.E.D isnt flashing and the ABS works perfectly. The Red L.E.D had also been flashing for the previous 3 years or so when the orange light came on the second time round. (I can't remember if the red L.E.D was flashing the first time the abs light came on and i can't remember if the L.E.D was flashing when we bought the car in 1998 with no faults- i was only 10 years old at the time and was far more interested in the Berlingo multispace and free sweets )

So if its not connected then why has it stopped flashing after the front nearside abs sensor was replaced?

Can't comment on later models but our car never had an immobiliser fitted (only one in the dealership that didnt) and the alarm was disconnected when the car was 5 years old. So i can't see it being related to that either to be honest. I feel really bad disputing what you're saying (see p.s) but bearing in mind our experiences i can't find a fault in our mechanics work/argument; replaced sensor = functioning abs and red L.E.D light off for the first time in years.

In any case, so as not to confuse Nick, i would definately make the nearside front sensor the first thing i checked.

Phil

P.S hello again malcolm! We'll have to stop meeting like this and meet in real life!! You may not remember but you gave me some excellent advice about clutch clips on our xantia on the ccc forum a few years back when our then 'mechanic' (not Graham Morton) was struggling with it. Anyway we sacked him after he misdiagnosed a strut top failure...and now use GM.

[xmexclusive]

Out of interest I turned out the Xantia books of wiring diagrams.
From those that I looked at there is no electrical connection shown to lamps other than the ABS warning lamp and that the ABS ECU takes one of its 4 power feeds from the brake light switch. Had never though to include brake pedal switch and brake light bulbs in an ABS fault test.
There is also a long running debate about the ABS on certain Citroen cars continuing to operate after the warning lamp is up. On both the Bendix and the Teves system on XM's it is reported that in this state low speed ABS release happens erroneously. I believe Citroen took the unusual step of issuing dealers with instructions to advise customers that they were mistaken should they try to report such a fault with their car. Many Citroen drivers rely on their cars high performance brakes reducing stopping distances to suit. Experiencing this unexpected release in the later stages of stopping can come as a bit of a surprise.
I would not recommend anyone continue to use a car with the ABS light up.

John

[CitroJim]

I would not recommend anyone continue to use a car with the ABS light up.

No, absolutely not John, I totally agree. Xantia brakes sans ABS are a bit lethal if you don't know them.

Many years ago back when I had just got my first Sinker I was unaware it even had ABS as there was no light and I did not yet know the car to spot it did in fact have ABS. Anyway, I happened to need to do a stop in a great hurry and far too easily locked up all four wheels and the end result could have been a bit messy; in the event all was good but...

I discovered the ABS light had been tampered with and there was a duff sensor. Replaced the sensor and with the ABS working i did some very heavy stops and the difference was night and day. The car just stopped on a sixpence with absolutely no drama at all. That's how it should be. Without ABS the brakes are far too keen to lock up.

The slow release is a very well-known problem and can have two causes. Either a weak sensor/dirty dragon's teeth causing a low amplitude signal which falls below the threshold at low speeds which the ECU erroneously interprets as the wheel in question being locked. The ECU then takes the appropriate action...

The other cause can be incorrect assembly of a front sensor where the heat shield tab or a washer is placed under the sensor securing hole which leads to an incorrect pole-piece to dragon's teeth separation distance which leads in turn to low output at low speeds and the same effect happening; the ECU believes the wheel is locked and releases the brakes.

I too looked at wiring diagrams and reached the same conclusion as you did John.

Phil, I might possibly have an explanation. On an older model there is a key-operated alarm defeat switch under the bonnet. Turn this on and neither the horn will sound nor lights will flash but the alarm can still be set and operate the LED indicator. As the alarm and any immobilser fitted are totally independent, except for the flashing light, you'd be blissfully unaware of a problem.

Later MK1 Xantias used a different alarm and the key defeat switch was deleted so this condition could not occur. MK2s were different again and here the alarm LED is in the Driver's door up by one of the ultrasonic sensors.

I guess your garage reset the alarm when they replaced the ABS sensor Phil.

[PhilGreaves]

lol do i feel bad- first time on and i start an argument! lol im not usually like this honest.

Well thats what ive been told and im sticking to it for the above reasons. Just seems too coincidental otherwise.

What i would say is though, you're presuming that those wiring diagrams are accurate? They may not be. When we had our drivers door solenoid done John Greaves (no relation*) said it would be simple as its "plugged in -points to wiring diagram-"....it wasnt plugged in the diagram (from Citroen) was wrong...a different story though..

I understand what you are saying but the Xantia is our main car and has been and will continue to be used regardless of the orange abs light is on. its perfectly safe in *our circumstances* and the abs defo works properly. We tested it to make sure- not to be advised really but its a quiet area and nobody was around.

Further to Jims post (soz hadnt seen it before) ive done two very harsh stops in the xantia recently; on neither occasion did the wheels lock up and the second time the abs did kick in- albeit briefly. The latter felt just like it did on my driving lesson when i accidently engaged the abs system. Although if im honest the xantia's felt better. (no both occasions i wasnt driving too fast and werent my fault). Thinking about it my dad did once use the key under bonnet to turn the alarm off. But the alarm broke about 10 years ago so hasnt been used/set since yet the L.E.D has been on in that time. Can't imagine the garage resetting it as they knew the alarm was broken- i can always check though.

I guess you'll have to see me at weatherby and find out for yourself if the abs works properly. (bottle of beer or a xantia bburago model on Graham/it working!! )

In any case from everything ive heard i wouldnt presume its an ecu fault/needs replacing and i would first look at (manually) the front nearside sensor as this in our case is always the ones that fails. Perhaps, for Nicks sake we can at least agree on that?! lol and i'll try to stop confusing the issue

Phil

*a long running joke of his, seems right to carry it on.

[CitroJim]

No worries at all Phil, we enjoy a good, lively discussion on here and may I belatedly perhaps, wish you a very warm welcome to our little community Note that a good discussion on here never turns into slanging match; just the presentation of facts and beliefs on the subject at hand

Wiring diagrams: yes, I see where you are coming from and if we confined our studies to the Haynes manual than yes, valid point but both John and I will have looked at the official Citroen diagrams and more than one too. I have four volumes of diagrams covering 1993 to 1998 and there are many significant variations between model years and models within those years. One diagram does not fit all where a Xantia is concerned even though Mr. Haynes might have you think so. He publishes only a very small sub-set...

In the case of a questionable ABS problem, the only answer is to get a Lexia Diagnostic onto it and do some live testing with the car under way and under braking to see exactly what is going on. Takes all the guesswork out of it.

I've sen slightly iffy sensors that are not bad enough to bring the light on claim the wheels are spinning at 50-odd kp/h even with the car in question up on ramps!

Finally, Citroen Hydraulic ABS does not work like conventional ABS. You do not know when it is in operation as there's no pedal feedback. It just does its job quietly, silently and with no shudders in the brake pedal department*...


*unless you've removed the pedal spring and then you might feel just a tadette of judder...

[xmexclusive]

Hi Phil

Do not take too seriously our banter about faults and the causes.
For many of us it is our learning process.
To be able to draw down on others people experience makes such a difference.

Hi Jim

Interested in what you say about the release problems.
Got a very nasty shock the other day when I researched the XM ABS waveform limits. They are so lax that I concluded that the ABS ECU could not use signal amplitude as its method of control but must use some form of signal transition. On the filling of the dragons teeth few people reaise that most of the muck is fine steel particals worn from the brake discs and this changes the waveform shape.

John

[CitroJim]

Absolutely, that's how we've always learned a lot of pretty deep stuff by these sort of discussions Not to mention similar discussions at various rallies and meetings... Gosh I'm looking forward to the start of the rally season....

John, yes, although amplitude is a function of speed, you're right, it'll be the frequency that's measured. The same applies to the speed sensors in the 4HP20 autobox and the manual contains some nice diagrams to show amplitude vs. speed and the related frequency vs. speed. The output speed sensor reads the teeth on the epicyclic output gear so the principle is exactly the same.

However, there comes a point when the amplitude becomes too low for the input circuits in the ECU to be able to process the raw and dirty sinewave signal from the sensor into a good, sharp, clean squarewave that the digital logic needs to be able to read its frequency and thus determine the wheel's speed. Effectively the digital signal will either fall to a constant logical 1 or 0 when the input signal falls too low which the ECU will interpret as a locked wheel. Amplitude is a function also of the distance of the sensor's pole-piece from the dragon's teeth and any dirt on these, especially metallic dirt, will reduce the amplitude. So will any small failings within the sensor such as shorted turns on the winding or high resistance within the winding.

The similar sensor in the 4HP20 has to be carefully shimmed to set the clearance between it and the output gear teeth.

EDIT. yes, a big build up of metallic dirt might even increase the effective number of teeth as seen by the sensor and cause the frequency to go up and thus give erroneous speed information!