Abs This Time ... Update

[citroenxm]

Hi All

Recently.. on here to .. I posted ABS problems I was having, that being orange light/ message constantly on HOW EVER the ABS working perfectly.

Last weekend, I fitted a ECU ABR unit from a 1990 H reg, 2.0 SEi car. Now what is happening now is Light OUT !! but, when I brake, and just getting a crawl the light comes on again!

Stop

Start off, 10 seconds later light cancels itself out

Ok. Should I then assume I'm looking as a sensor thats close engough to the ABS ring to keep the light out on check.. but too far away to function properly when called to check wheel rotation??

I did notice a rather larger then normal gap on FRONT PASSENGER side sensor. Should I try moving the sensor on it adjuster in a little??

Nice to see the light out at last!

Regards
citroenxm

[noz]

Hi citroenxm,

Good to have you back!!

Just a thought, have you ever tried to test for a good 12v and an earth at the abs ecu. I'm just wondering if a dodgy power supply is giving you the sporadic symptoms. As I say, just a thought.

Cheers

noz

[citroenxm]

Hi noz

Thanks, good to be back...

Which pins do i need to test on??

Regards
citroenxm

[noz]

Hi citroenxm,

Can you identify the make and model of your ABS system or ecu? Bosch, Teves?

Cheers

noz

[citroenxm]

Hi Noz

Its the BENDIX ABR Siemans, NOT the tevis. Didn't think XM's had bosch systems.

Sensors have Square Green plugs on the ends of them to connect to car.

Regards
citroenxm

[Ciaran]

Funny you should mention it CitroenXm, I have a similar intermittent ABS issue, which I'm beginning to suspect is related to the rear wheel on the driver's side, as the problem gets better or worsens anytime that wheel is disturbed.

It does things like coming on in traffic after sudden movement (like tonight for example, on the start-stop 'motorway', my foot slipped off the clutch slightly, and the car lurched forward somewhat, causing the ABS light to come on immediately, and remain lit for the rest of the journey home. That's the first time it's done it in about a week mind you, but the frustrating thing is just when you think it's cured itself, it comes back!
The ABS does work mind you, as I had cause to test it a few weekends ago...

[techmanagain]

Snap! I don't know why mine does the same thing, either. I sent it in for MOT and it came back clear, whereas it had been intermittent for yonks before, and is still doing it. I'll deal with it when the next MOT is due - promise!

[Ciaran]

Speaking of MOT's, mine first started really exhibiting these ABS symptoms, when I started it up.....to drive to the test centre!!
It had sat around for months while I got the time and funds together to get it ready, and had never shown so much as a glimmer from the ABS light in all that time.

In a blind panic I turned the ignition on and off several times, and the light finally turned off.... I drove there as softly as possible, praying it wouldn't come back on. As it turns out, I had plenty to keep me busy, when I discovered that the headlights weren't working.... after I'd been called into the queue in the lane!!

This post has been edited by Ciaran on October 17, 2006 11:18 pm

[citroenxm]

Hi all

Well guys.. further testing, and I think I have a solution.

I think the problem is a sensor TOO FAR away from the ABS ring....

Drive along slow down, then at a crawl, IE: catching traffic light traffic, I used my HAND BRAKE to slow and then momentum to stop - BEEP abs light on!!

It does still cancel itself though after starting off.. As mentioned above, my front passenger sensor has a larger then normal gap between sensor and ring, so shall set on adjusting the sensor inwards. Then see what happens then.

I think that becasuse the sensor is slightly too far away from the ring it cannot detect at low speeds, but at higher speeds enough of a field it created for it to detect movment.. HOW DOES THAT SOUND.... ??

Shall keep informed when I do it. I may try and adjust it before I take the car off the road for a rest for repairs!

Regards
citroenxm

[noz]

Hi citroenxm,

Hmmm. doesn't sound likely I'm afraid. When the car is stationary (the ecu can tell its stationary because none of the 4 wheel sensors are sending any pulses) the ecu can only check for simple resistance. In fact it does this every time the car starts. However this can take several seconds to complete this test. If you move off whilst in the middle of this checking process (the ecu can tell you're moving because it now sees pulses from one or more sensors) the resistance test is abandoned. It is abandoned until the next time you come to a rest or the ignition is turned off. Thus the light normally comes on at traffic lights or waiting to enter a roundabout. Switch the ignition off at the lights and then restart just before you move off. The light will stay out until the next time you come to a standstill.

The problem therefore is that one of your sensors has either a permanent or intermittent resistance problem. Have you measured the resistances of all 4 sensors from the multiplug on the ecu? (probably my fault for not providing the wiring pinouts). They should read about 1000 to 1100 Ohms each. If they check out OK then have someone waggle the cables under the car whilst you keep on measuring the resistance. Hopefuly an intermittent fault will show up at this time.

Sorry if thats not what you wanted to hear. I'll try to look out the correct diagram tonight when I get home form work (whenever that will be !!).

Cheers

noz

[xmexclusive]

Hi Noz, Citroen XM and All

I think Citroen XM is on the right track as I believe that the ABS ECU does further regular checks that the system is in good order while there is no brake application and the car is moving. During this situation it counts the pulses from each sensor for a fixed period. If the counts do not agree the ECU causes the ABS light to flicker on. After a certain number of further misscounts the ECU switches out the ABS and puts the light on permanently. At next ignition switch on the startup static test clears the ABS and it starts working again and the whole misscounting process starts again. In my experience there is some randomness in how soon the ABS light takes to reappear, anything from 5 to 150 miles.

In my experience (from when I used to work for a living) the positioning of proximity sensors to the metal they are detecting is absolutely critical. Muck in the air space between the teeth is unimportant unless it contains metal debris. Unfortunately there is plenty of this from the brake pads and disks so cleaning the toothed wheels are worth doing if they are clogged up.

If anyone has more information or references on the detailed working and programmes for ABS units I would be very interested.

Regards

XMexc

[citroenxm]

Hi Noz

~Thanks for reply, however, the ABS light comes on while crawling, say 1mph!!

Not stationary..

Even without useing the brake pedal, but when slowing with the "hand brake"

Xmexec..

Welcome back, we have missed your input and noticed your abcense..

Hope all is well

Thankyou for your input to.. We shall get there I'm sure..

My next thing to try if adjusting sensors doesn't work, will be to swap All sensors from a spare car I have aquired with Working ABS system..

Of course, though, I shall check the resistance at ECU as sugested by Noz, and report back.

Regards
citroenxm