X-type 3.0 petrol.2004 How do i test abs sensors.

[madmechanic0774]

 I had this jag in today,

 The owner told me as he was driving yesterday the abs light came on followed shortly after by the EML.

I plugged in with solus pro and could only communicate through EOBD.

It came up with P1111.

I couldn,t access ABS system so tried the method of disconnecting each sensor individually and using the multimetre to perform a
knodes test.

All four sensors showed no resistance.

I wrote a post earlier but got the subject line wrong and it got locked, I can't figure how to paste the text so this is my result.
 Sorry for the mess Derek.

I did get a reply in this post saying i will have blown the sensors By performing a knodes test

As far as i was aware there is barely any current used doing this.

Inductive sensors? How should you test these? They appear the same as normal sensors.

If anyone can explain things and help me understand i would appretiate this.

  Regards Brad

[TopGun]

Brad,

You still need to add the year to the subject line to conform to the rules. And avoid the post being locked! 

[madmechanic0774]

Thanks Topgun,
                    Ive been having one of those days!
   Thank god its nearly finished, Hope tommorrows better.

  By the looks of this i don't think it will be!

[laldog]

http://www.mercedestechstore.com/pdfs/327_traction_and_braking/327%20HO%2002%20ABS%20(WJB,GC)%2002-25-04.pdf

Merc but they are all the same.

[ellipse]

i was reading the above and was wondering what a knodes test was ?, reading initial post it seems it is just a simple resistance check but ive never heard of it called that before so my curiosity side is kicking in

[Shuggy]

me neither ?? i was wondering myself    ..also can you test with an lcr meter ..or will that fubar the sensor too ?

[madmechanic0774]

Hi im Back again,
                 Thanks Laldog a great link there, i also found a similar one regarding how to test these sensors.

 Me calling this a Knodes test is what one of the lads i work with calls it and always has. I thought that must be its proper name.

I have always called it" checking the rissistance"

Anyway lets get back to my learning curve.

  I checked all the sensors this morning(the way i should have this time)

R/R wheel sensor unresponsive all the rest are fine!

Sensor on its way will be here tommorow.
Iv'e arranged for my mate to come round and with his launch to reset lights after fitting.


The one question i still have is" do you actually send a current of any kind down a sensor while testing with sensor unplugged
using a multimeter at 2k or even on volts?"
I believe not am i wrong?

Regards Brad

[Shuggy]

not too sure about hat but i always test  them with the LCR meter i hope that they are ok with that ?? i had a ford ka recently with these sensors (unbeknown to me ) i tested the two front sensors the resistance value was all over the place ? but the good one survived i even tested the new one  i bought with the lcr meter it worked afterwards ? but maybe i was lucky .can anyone confirm if its not good for them ? but live data if you can get it is maybe the safest option 

[laldog]

Well i use a scope cos i was told a meter "could" destroy them.

[Geo]

I always test these with a handheld scope (glorified multimeter basically) while they are connected. You can then see the nice square wave shown in the link laldog posted   

I find it is normally a wheel bearing problem with them rather than a sensor problem. I actually don't think I have ever found a faulty sensor on one but I have changed lots of bearings. Maybe I just haven't seen enough of them