ABS warning light on....

stevetheskaterboy · Post by **stevetheskaterboy** » 14 Oct 2009, 16:04

The abs light on my xantia came on this morn when i started it, its still there, fuses are fine

help lol

marsalek · Post by **marsalek** » 14 Oct 2009, 16:21

One of the four wheel sensors or the cables may be broken. Take care, at low speeds (like below 20 km/h) the broken ABS might deteriorate the performance of the brakes (in other words - it does not brake at all!). Until you solve the issue, I would recommend to remove the ABS fuse.

On the ABS ECU you can measure the resistance of all four sensors. It should read something about 1100 Ohm.

Karel

stevetheskaterboy · Post by **stevetheskaterboy** » 14 Oct 2009, 16:27

Ok ill do that, as i said it was great yesterday, grrrr!

Im going on holiday with it in two weeks, will it be sorted by then do you think?

Stempy · Post by **Stempy** » 14 Oct 2009, 16:33

Well if it's just a corroded connector, which is common, then no probs. If a sensor has gone it can be a bit of a song and dance to remove them, especially the rear ones. The bolts are generally rusted solid and the routing of the rear cables makes it awkward to remove and refit. Be prepared to swear a bit.

stevetheskaterboy · Post by **stevetheskaterboy** » 14 Oct 2009, 16:40

righty, ill start in a bit, its been one of those sot of days lol

VertVega · Post by **VertVega** » 14 Oct 2009, 16:55

Here is a piccy from a measurement. They give readings average lets say around 1050 Ω.
As seen in close up, meter is switched to resistance region and scale 2000 Ω which would be enough for reading an ABS sensor.

As Stempy says especially rear ones can be really difficult to remove and the rear route is very challenging which goes through the rear arm

PS: Marsalek, nice to hear from you again. You've not been around for a long time

red_dwarfers · Post by **red_dwarfers** » 14 Oct 2009, 17:30

Have a look at this thread for details on which pins to measure and some tips on renewing a rear ABS sensor if required

Im placing my bets on the problem being the NSF sensor

marsalek · Post by **marsalek** » 14 Oct 2009, 17:32

VertVega wrote:PS: Marsalek, nice to hear from you again. You've not been around for a long time

Hi, was on holidays with my ABS light on

(around 5000 km through the eastern Europe).

Here are the pin numbers for Mk1 and Mk2.

X1:
Front Left Pins Nr. 15 und 30
Rear Left 19 + 28
Front Right 1 + 6
Rear Right 29 + 31

X2:
Front Left 1 + 2
Rear Left 5 + 6
Front Right 19 + 20
Rear Right 22 + 23

Karel

stevetheskaterboy · Post by **stevetheskaterboy** » 14 Oct 2009, 18:46

i have just checked the readin and they are all average, along with there doesnt appear to be any visual problems, should I go to my local garage and ask for a diagnosic?

luckily I am a regular customer (with my learner car, which was my dads) so they do it for £15 a pop

VertVega · Post by **VertVega** » 14 Oct 2009, 19:04

Diagnostic tester will only tell you something like "Speed Sensor Error" but still not tell exactly which one of the four caused that.
Someone, please correct me if I'm wrong.

If readings were good then you should drive for about at least 200 m (speed goes over 20 km/h) then ABS light should turn off.
One of the sensors is giving signals of a future replacement

If the light doesn't turn off then the other options are like: cracked or loose toothed ring, dirt on toothed ring, weakened wire, corrosion and etc.

stevetheskaterboy · Post by **stevetheskaterboy** » 14 Oct 2009, 19:35

Gotta love technology lol, I am going to take it out for a while later and see what happens.

Ive cleaned most of the conections, checked fuses and checked for visual damage and checked reading, think the good old random might be involved!

I will keep you all informed later, and thank you all for being so understanding, its great having so much information and advice on tap, and from such a great group

Stempy · Post by **Stempy** » 14 Oct 2009, 21:00

I think the ecu test sequence first checks the static impedance of the sensors, if all is well it will turn off the warning light.

Then when you start to drive it is looking for pulses from the sensor as the wheel turns, if the pulses aren't up to spec then it will illuminate the warning light.

If you substitute a 1k resistor for each of the sensors in turn you can isolate the faulty one as it will pass the static test and only illuminate the light as you drive off due to the lack of pulses..

Post by **CitroJim** » 14 Oct 2009, 22:08

A pukka Lexia diagnostic will pinpoint the problem exactly. Off-times it will show a slightly duff sensor indicating a wheel is spinning at some silly number of km/h even when stopped!

stevetheskaterboy · Post by **stevetheskaterboy** » 14 Oct 2009, 23:42

Good news!

I took the car out for a bit, put it through the jet wash then took it for a blast up the M6, then the light went out.

Then when noone was around I did a emergency stop at 70mph, the abs is very odviously working well lol

marsalek · Post by **marsalek** » 15 Oct 2009, 08:10

Hm, 70 mph...

Due to the electromagnetic nature of the sensor's functioning, the higher the speed, the stronger the signal is. So if there is some dirt on the sensor or the ABS ring, the signal is deteoriated usually at low speeds.

Karel