ABS light on

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glenndaleuk1
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ABS light on

Post by glenndaleuk1 »

1997 xantia 1.9 td vsx 93000 miles

Hi all
I am having a problem with the ABS light staying on. About a year ago the light came on I checked the readings on the ECU which said it was the nearside front that was causing the problem, however a little while later it repaired itself, so I didn’t investigate further. About a month ago I had eight new spheres fitted and on the way home the ABS light started to flash, then after a while it stayed on. I left it for a few weeks to see if it repaired itself again unfortunately it hasn’t. On checking the ECU again I have found the n/s front is ok and the other three sensors are dead which is a complete reversal of the earlier readings. I suspect it may be a plug that is at fault my thinking being that something may have been disturbed when the spheres were fitted especially as three sensors have gone of at once. Although I may of course be completely wrong as it was a couple of weeks before I actually checked the ECU. I would appreciate any thoughts on the matter or does anyone know if there is a connecter that may cause three sensors to go off. Thanks in advance

Glenn
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Post by dnsey »

Pure speculation, but if the N/S/F sensor has become intermittent, it may be generating spurious pulses, which could in turn fool the ECU into thinking that it's missing corresponding pulses from the other wheels.
Ideally, if you have access to an oscilloscope (a basic scope application running on a laptop would do), you could do with checking the outut from each sensor to be sure.
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Post by reblack68 »

Are you sure you're checking the right pins? My last job was in electronics and it wasn't unknown for me to spend hours chasing a fault that wasn't really there because I'd counted pins from the wrong end or something equally silly.
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Post by AndersDK »

reblack68 wrote:... because I'd counted pins from the wrong end or something equally silly.
\:D/ :^o :-# :lol:
Anders (DK) - '90 BX16Image
glenndaleuk1
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Post by glenndaleuk1 »

Thanks for the replies I will check the connectors and pins again late in the week.
I`v just been reading about ecu and apparently if the light comes on and stays on then its the ecu at fault and needs an exchange or a repair. I`m not sure how acurate that is, and I would hate to fit an exchange unit just to find the fault still there. None of the suppliers actually mentions checking the old unit first. So what are you supposed to do ? Thanks again

Glenn
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reblack68
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Post by reblack68 »

The ECU isn't that hard to remove is it? Surely you could persuade another Xantia owner to let you plug it into their car and see if it works.

You certainly shouldn't think about replacing the ECU until you have satisfactory resistance readings from all four wheel sensors.

One thing to check, which hasn't been mentioned up till now, is that the "dragon's teeth" are still there. Mine shed the ring and I only discovered what was wrong when I was looking under the car for something else.
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Post by reblack68 »

superloopy1 wrote:My understanding (and I have an ABS light on at the minute :oops: ) is that the ECU is rarely at fault if on switching on, the light 'flickers' which means it is doing its own internal self-test and has found a fault, more than likely a sensor.

If however, on watching the light, it is on and doesn't flicker, staying moreorless solid, then my chap, you may well have a dodgy ECU.

Hope this helps.
That only applies to the older ones. The old ones reset themselves when you switch the ignition on, the later ones reset when you hit about 20mph and I don't think they do the flickering thing. I'm not sure when the change happened, my early '97 model has the old type.
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glenndaleuk1
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Post by glenndaleuk1 »

Thanks for the help chaps. I just ckecked the pins again and getting the same readings. Don`t know anyone in Manchester with an xantia. On switching the ignition on the light does flicker for about two seconds then stays on solid and stays solid. Not sure if this means anything though. I don`t know enough about the subject.

Glenn
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Post by reblack68 »

Here are the pin numbers from a previous thread.
SimonT wrote:
slim123 wrote:For the sensors and as Andrew says it will probabally be one, try this.

Ensure ignition is off.
Unplug the muliti plug from the ABS ECU.
Use an OHM meter to take these readings.

Pins No 15 and 30 = Left hand front sensor

Pins No 1 and 6 = Right hand front sensor

Pins No 19 and 28 = Left hand rear sensor

Pins No 29 and 31 = Right hand rear sensor.

All readings should be 1080 OHMS approx, in reality if you get no reading then the sensor is duff. But it is allways worth cleaning the connections.

If you shine a maglight at the pins you should be able to see the numbers of the pins.

Good Luck
Slim
Done a little drawing of the pinouts too if this helps anyone
Image[/img]
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Post by MikeT »

I'm wondering if the wiring is different for some models. When I manually tested my old Mk1 ABS system, I found three failures yet a diagnostic machine later identified the good one as being bad :?

I'm afraid I didn't get it repaired and sold the car so can't say who was right there but I did double-check my findings as they seemed too absurd.

It's more likely to be user-error though :lol: :oops:
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Post by reblack68 »

Here's the later version.

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glenndaleuk1
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Post by glenndaleuk1 »

Mines the drawing and yes I am testing the unit and not the plug. It looks difercult to make a mistake on this one as the drawing shows the top line is longer than the other two. I have checked it three times now and get the same readings. I am at a loss as what to do next.

Glenn
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Post by CitroJim »

superloopy1 wrote:Guys .... jog my memory here. It is the plug that should be tested here
Yes, it's the plug that you should be testing.. You'll get some very strange results trying to test into the ECU itself.
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glenndaleuk1
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Post by glenndaleuk1 »

I`ll have another look at it later, looks like I have been testing the wrong bit.
glenndaleuk1
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Post by glenndaleuk1 »

looks like I may be brain dead testing the wrong bit. It`s pretty obvious when you think about it. anyway checked them again and found 15and 30 dead which I think is n/s front which is the one that gave me trouble then repaired itself last time,funny thing is i must have checked it properly last time. Brain cells must be deminashing faster than I thought.. So I will check the connector I may get lucky.
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