A B S Light

ucavic · Post by **ucavic** » 09 Oct 2003, 21:06

Hello Good People of this World,
I found this topic to be really close to my problem. I have a 1993 2.0i Xantia and since recently (last month or so) my ABS light NEVER goes off.
On and off for the last year the light wouldn't turn off after start and would then turn off while driving, but it would never turn on while driving. Lately it is just on all the time.
From the posts I gather it is not the sensors, it would be the ABS controller?
Guys at the service shop probably know that a new ECU is too expensive to buy, so they came up with some excuses about some mismatch between sensors and ECU... They also told me the sensors alone were ok.
Any suggestions? Can I probe the sensors myself? Is there a list of pins on the ECU where I can check for resistancy of sensors? Should I send the ECU to be fixed or remanufactured?
Any help would be appreciated... Thanx, Uros.

Homer · Post by **Homer** » 10 Oct 2003, 00:56

If the light stays on for more than the usual time (a few seconds) then it should not go out again while driving.

adrianeaton · Post by **adrianeaton** » 10 Oct 2003, 19:37

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by acrowot

Hello Jeremy, the brakes are fine when the light is showing ie. ABS diasabled, it is when the light is not showing that the brakes malfunction and then just before the car stops, but it does not do this all the time.
<hr height="1" noshade id="quote"></blockquote id="quote">
My BX 16V did EXACTLY the same thing you describe - ABS light would do its normal check on start up and would normally go out, sometimes it wouldn't. More often than not I would only get the other symptoms you describe where the brakes would judder as I came to a halt, almost always at junctions where the wheels were being turned slightly off centre. This would happen at low speed and low pedal pressure.
Eventually the problem got worse and the light was more on than off and eventually I got it checked out. It turned out to be the NS front sensor, which had missing insulation near the battery tray and was earthing on the inner wing under various conditions.
To check the front sensors properly you need to jack the car up and turn the steering while monitoring the resistance - if there's an intermitant connection this should show it up.
The ABS light would also go back out again after lighting, although not always - this is because the fault would 'clear' while driving and the system will reset. If the fault appeared at rest it would usually stay on.
10 quid on a 2nd hand sensor and it's given no trouble at all since.
Hope that helps
Adrian

NiSk · Post by **NiSk** » 10 Oct 2003, 20:54

John, your experience is exactly as mine was with my '93 XM TD12. Fault = front n/s ABS sensor. It's not that difficult to check out the sensors: Find the ABS computer, disconnect the large bendix plug and measure the resistance between the wire pairs to the sensors. I'm betting you'll find at least one with o/c or at least a lot more than the 1000 - 1500 ohms it should have. Where the fault actually lies is then the grubby bit!
//NiSk

acrowot · Post by **acrowot** » 11 Oct 2003, 02:06

Thank you to all who responded to my cry for help. All my sensors checked out ok resistance wise. The last thing I tried was to remove the plug from the ECU I then cleaned the contacts and put a slight twist in each active pin reinserted the plug and all was fine for about 10 days. I was then sideswiped at some traffic lights and my Xantia has been in the body shop since, I should get it back next week so I am not sure if the fault is cleared or not. I did buy a second hand ECU (£20.00) so if the problem comes back I will change the ECU which also came with the valve block.

alan s · Post by **alan s** » 11 Oct 2003, 04:45

It would appear that a sound investment for you could be a spray can of electronic contact cleaner.
Do the plug & the pins & I'd reckon you could all live happily ever after.
If it's not working after it comes back from the panel shop & assuming it's an insurance job a "Mister what did ya do to me car?" type question may get the insurance to check it out could be a worthwhile move.[;)][;)]
As I said earlier in the piece, I thought it was an internal break and the results after doing the plug almost proves it, but in the wiring & not the sensors as I suggested. It could also mean that after a hit, it could start playing up again so claiming it via the insurance would be quite legit.
Alan S [:D]

kafkaian · Post by **kafkaian** » 11 Mar 2005, 13:28

Well, having resolved nearly all the problems on my car over the last week (and thanks once again to this forum for giving me the faith not to just scrap a perfectly good car), I suspect my ABS ECU has failed. To be frank, since new, the ABS on this car has always had a problem. I took the car to my very good Cit trained mechanic and he says he will have to do a proper ECU check at a dealership. Recon ECU GBP220 (Eeeeek :vomit: Oh Gawd

)

FrenchLeave · Post by **FrenchLeave** » 11 Mar 2005, 20:15

I am disturbed by Jeremy's statement that the ABS is designed not to work at slow speeds, you can slide a long way if you lock your wheels on ice at 10 mph. Can anybody explain why this feature has been designed in?

Kowalski · Post by **Kowalski** » 11 Mar 2005, 20:29

ABS stops the wheels from locking. If you are trying to stop the car rather than slow it down, eventually you want the wheels to stop turning. If the ABS didn't have a cutoff speed it would never allow you stop the car, that would be bad.

ACTIVE8 · Post by **ACTIVE8** » 11 Mar 2005, 23:39

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Kowalski

ABS stops the wheels from locking. If you are trying to stop the car rather than slow it down, eventually you want the wheels to stop turning. If the ABS didn't have a cutoff speed it would never allow you stop the car, that would be bad.
<hr height="1" noshade id="quote"></blockquote id="quote">
The A.B.S. electronic control unit also needs to know when the car is moving, and a trigger speed needs to be present, to allow it to work properly.
A.B.S. also links into E.S.P. on the very latest vehicles, and will cut back the power, and if a wheel is spinning apply the brake on that particular wheel. Without the trigger speed then the E.S.P. would keep cutting in.

pwatson · Post by **pwatson** » 12 Mar 2005, 00:07

Be careful about jumping to the conclusion that the ECU has "gone". A couple of years ago I went to our local independent with the ABS light on on our 1993 Xantia and said that I hoped it wasn't the ECU. His reply was that in 10 years of looking after Xantias he had yet to replace an ABS ECU - it was almost invariably the sensor - usually the front nearside, or the wiring. In our caes it ws the nearside sensor - replaced for £75. OK maybe I could have done it myself cheaper but my wife regarded it as "her" car and she paid!!! Did I object?

acrowot · Post by **acrowot** » 12 Mar 2005, 19:50

In my case it was the ECU, since changing it some 16 months ago I have had no further trouble.

Mark8 · Post by **Mark8** » 16 Mar 2005, 22:12

Traced and replaced the fos sensor on my xantia 1.9td......£25 from the scrappy [:0]
I'm in the wrong buisness........although it's a small price to pay for safety [:D]

FrenchLeave · Post by **FrenchLeave** » 17 Mar 2005, 04:32

Thank you Kowalski and Active8, I learn something new every day.