Rear ABS Sensor Connectors

[rg]

Folks,

Great to know that the forum is back up and running! Well done, Norrie!

Meanwhile, I may have to replace one of the rear ABS sensors. I have a vague memory of the connectors sitting on top of the subframe. Can anyone give me any pointers on ease of access?

r

[xmexclusive]

Hi rg

Spot on.
Getting at the passenger side one is easy if you drop the subframe on that side.
Still a lot of work. Drivers side cannot be dropped far enough as it fouls the fuel tank filler pipe. Just done the rear sensors on an M reg 2.5 estate (Bendix ABS, how I hate unreliable Bendix). Short life car, particularly if it fails the MOT, so I decided to go for a quick fix. Found a length of scrap 3.5mm pipe, bent the end into a hook and used it to rip the sensor plug/wiring out from on top the subframe. Cut the ABS wiring in front of the fuel tank and rewired it putting the sensor connectors inside the subframe. Easy access in future. Simply wheel off just like the front. You need to use the same twisted pair wire, mine came from a scrap XM. While doing this I found that I could use a 1.2 k resistor in place of a sensor to confirm the ABS start up routine would put the light out.

John

This post has been edited by xmexclusive on August 22, 2010 11:05 pm

[Jan-hendrik]

QUOTE

(Bendix ABS, how I hate unreliable Bendix)

A few days ago I read this on xM-L:

Do not need to reset, it will clear it's fault when everything fine.
However teves is a crap system, front sensors die usually (weak/cheap
cables), and the relay/relay socket itself is terrible (behind the front
left lamp) and the ecu itself is a weak design too.

So which system is worse

[rg]

Thanks, chaps!

The XM-L post was in response to mine in respect of ABS light. Which leads me to the question:- I've just done the front ones, and they test up with resistance within limits. However, the light is still on. The car is stillon blocks. Should it go out when the system finds the correct resistance from the sensors, or does it have to sense wheel rotation? It's so long since I did the last one that I can't remember! Opinions on XM-L seem to vary. It's a Teves system.

rg

[bobhalliday]

Hi RG.

I had lots of trouble with my 2.1 XM Estate 1996 rear Bendix ABS. The last time I removed spare wheel and carrier, cross over exhaust section, and that helped me get two hands up to the drivers side wiring easy. I did want to cut off the plug and hard wire it and make it easy to get to in future but the wires coming out of the loom are so short that I was afraid to cut them in case they just disapeared into the loom! All that was over a year since so it's worked fine so far!

Bob.

[kenhall1202]

Hi rg,

I recall replacing a rear Teves ABS sensor with a second hand one and the light stayed on until I had driven the car a few hundred yards (great sigh of relief!). The Teves ECU checks for valid resistances from all four sensors at rest but will still display a previous fault (ie light stays on), if when the car was last used the ECU was not seeing a/c signals from all four sensors. With a duff sensor the ABS function shuts down and the warning light stays on.

Ken

This post has been edited by kenhall1202 on August 23, 2010 02:31 pm

[xmexclusive]

rg

The start up test is a static test of coil resistance value only.
It does not require any wheel rotation, if fact while checking things out with the car on blocks I added the test resistor to the wires by the ECU. The ABS light flashed correctly then went out first try and then every time thereafter.

J-H

Both Bendix and Teves front sensor wires are equally prone to fatigue damage and it is very difficult to spot as it usually gives intemmittant open circuit from vibration while on the move. Restarting the car often clears the ECU so this fault give the random ABS out of use during a run. I have been modifying my front sensor cables for some time now so that they are less subject to vibration.
As far as the ABS types are concerned neither Bendix nor Teves became the PSA system of choice. Hence the spares difficulty and high price. Teves is at least 5 years more recent in electronic design terms. It has a much faster core processor so has a better developed operating progam. The downside is that its system checks are more frequent and it records a wider range of faults.
I am convinced that the Bendix can permit wrong side system failures so it is not my system of choice.

John

[noz]

Hi all,

As a further point, when you jack one of the front wheels off the ground, start the engine, engage a gear and rotate just the one wheel off the ground, the ABS ecu gets very confused. It thinks the car is travelling because it gets a signal from the distance sensor but it sees that three of the wheels are not turning. It also knows you are not pressing the brake pedal. So the only conclusion it can reach is that three of the wheel sensors are broken and records the errors as such in the ecu memory. The ABS light should be illuminated on the dash at this point. Once finished, the ecu memory can be accesssed with the Lexia and the the stored errors erased.

From my experience the light on the dash will light if there is a current fault meaning a fault present at that moment. If that fault goes away e.g. from the example above the car is lowered onto all 4 wheels and then driven, then the light goes out but the record of the fault(s) is(are) retained by the ecu. The light on the dash does not stay lit if the fault which caused it to illuminate has since gone away.

As a further observation, if you have a faulty sensor, start the engine and move off immediately whilst the ABS ecu is still performing its resistance checks then the resistance check seems to be aborted. However, when you arrive at the next junction, traffic lights or queue and the car comes to a rest then the ecu perfoms the resistance check again. If one of the sensors fail the check at this point then it will let you know by illuminating the warning light on the dash. Switching off and restarting temporarily removes the warning. I have no idea whether the ABS physically functions during this time. Thankfully, I don't use it (much!).

Cheers

noz

[rg]

Thanks, Noz.

Lo and behold, driving off for the MOT today, the light went out in around 50 yards. And stayed out. Hallelujah! I really was not looking forward to changing the rear sensors.

However, it failed the MOT on underbody rot and a leaking pinion valve. I can post more details if anyone can suggest the correct section of the forum.

r

[noz]

hi rg,

Sorry to hear that. I had similar trouble with the rack recently.

General issues is probably the right place since neither faults are really related to late 2.5's or V6's.

Cheers

noz

[xmexclusive]

Hi Noz

The Bendix start up test takes 3 seconds.
There is a minimum car speed for the ABS to cut in.
Teves being a later design will be faster with its tests.
If you manage to interupt the start up test then the system should fail with the light on.
Something that Citroenxm showed me about the Bendix is that if the warning light has come on while the car is moving then give the ignition switch a careful flick towards the starter position. This cuts one of the 12v feeds to the ABS ECU. The ECU then carries out a full start up test and if this is ok the light goes out.
That I think proves that the start up test continues and completes with a moving car.

John

This post has been edited by xmexclusive on August 25, 2010 09:06 am

[Norman]

Hi All,
When i had the spheres replaced at Plaides one or more of the wheels was rotated off the ground, when it was back on the ground and the engine started and taken for a test drive the Abs light was on but turned itself off after a short distance.
At the National Rally Citrojim put his lexia on to check for faults and it came back with none, so does the abs circuit clear its faults after a restart ?

Regards,
Norman

[xmexclusive]

Norman

The ABS has the ability to store both permanent and temporary faults.
Its programme also ranks them by risk level.
It can also monitor and record the frequency by which they occour.
The temporary faults get cleared on switch on of the ignition to start the car.
It will retain the record of serious faults during switch off.
Taking the example above with a Bendix system.
Ignition switch on clears temp faults and proves the system good.
A Lexia reading could then show no faults recorded.
Suppose the car sometimes puts up the warning light while travelling.
A Lexia reading would then show intemittant fault on a sensor.
System would treat this as a temporary fault and keep clearing the light on start up.
Repairing the faulty sensor or wire and the ECU will purge itself with no need to clear with a Lexia.
Now suppose you continue with the faulty sensor present. Each time the warning light appears you apply the flick the ignition switch while moving. This clears the stored temporary fault but the ECU makes a note that it lost one of its power feeds while running. It records this as a permanent fault.
It will also move up to the next notch in its risk programme and the warning light will appear more frequently or even permanently.
So you eventually repair the defective sensor but make no Lexia reading.
The ECU still retains the permanent fault records and will treat any temporary fault it sees as high risk. System will be much more prone to putting the light up than it should be. Lexia reading will purge the ECU and return all to normal.

John

[noz]

Hi John,

Well every day is a school day as they say.

I have two questions:
1) How did you find out about the inner workings of the ECUs? Do you have access to technical info on the programming?

2) You used the phrase "Permanent Fault". This is exactly the phrase I get when I plug the Lexia into my engine ECU. No matter how many times I clear the fault the "Permanent Fault" remains. I am still able to see live values and I have one experience of having an air temperature fault which it displayed and I successfully cleared. Do you have a similar in-depth knowledge of the engine ECU which may shed some light on this? ( I don't want to hijack an ABS thread and turn it into an engine thread but if this is worth discussing elsewhere we should start a new thread.)

Cheers

noz

[xmexclusive]

Hi Noz

Been collecting PSA manuals for quite a while now usually in job lots.
Tended to flip through and extract the folders of interest so have binders for Engines, Gearboxes, 2.5TD's and ABS as well as the 13 binders in the XM series.
My memory is not the best and my technical understanding often lacking so keeping track or what there is and putting my finger on the wanted information is not easy.
This summer I have finally made room in the house, mainly roof space for the bulk of them. Previously a lot of them occupied the backs of two of the SORN cars. Working through systematically cataloguing them so I know what I have got and can find them.
I have surprisingly found the Peugeot (Spit) manuals very interesting as they are by no means direct copies of the equivalent Citroen ones. I was only collecting these in the hope of information on cross use of spares. A lot of the ABS information has come from PUG booklets. Will see what I can turn out. There is something somewhere about the 2.5 ECU counting faults down from 40 to zero. The 2.5 PUG 605 using the injector nozzel types differently that I sent you came from one of those manuals.
Another item worth mentioning is that we have now got the 2.5 running (limp) that Techmanagain asked for helpers on. Main trouble was wrong ECU version and incompatible glowplug relay.
Sorry about wandering threads but will try to add some of the ABS stuff here to compensate.

John