Abs Fault

[boromike]

Hi all

 

looking for some help on my 1999 2.3 Gal. I have the ABS light permanantly on so following various threads in this excellent site I have done some DIY testing on the two front sensors.

 

The problem is I get open circuit on both sensors, now it could be that both sensors are u/s or is it possible that I have a different sensor type than the magnetic switch type. Looking at the sensor it is sited to 'read' a toothed ring on the whhel itself - if this helps with its identification.

 

Cheers Mike.

[johnb80]

How are you testing them? It should be with a multimeter set to resistance. If by any chance you're using a test lamp it may not show through the sensor.

 

Regards - John

[boromike]

John

 

Thanks for the interest, I am using a multimeter and getting open circuit.

 

Cheers Mike.

[johnb80]

Then it would seem you have found the fault(s) !

 

Regards - JB

[Guest j_mchattie]

Sorry if im showing up my lack of ABS knowledge (i dont have it fitted), but the mention of magnetic sensors made me think that the circuit would be normally open. Then as the 'teeth' go past the sensor, it would turn on and off as each passes.

 

So normally, you would have no reading when the sensor is off the car (zero resistance), but when a magnet is nearby - you would get resistance.

 

Or have I just made a fool of myself?

[seatkid]

Or have I just made a fool of myself?

:lol:

 

IIRC the sensor is a pickup coil (with embedded magnet) - a bit like a guitar pickup... it generates a small AC voltage as the teeth fly by. So using a multimeter you see the resistance of the coil. Open circuit indicates a broken sensor.

[boromike]

Apologies for wasteing peoples time, I had a dodgy test lead, I have retested all sensors with readings of about 100kohm. So from previous threads on the subject I reckon the sensors are all OK and its the ECU which is at fault, this is going to be expensive !!!

 

Cheers Mike.

[Guest j_mchattie]

Oh ok.

 

I thought it would be a magnet that gets attracted to the teeth as they go past and so closes a switch.

 

Thanks

[johnb80]

Oh ok.

 

I thought it would be a magnet that gets attracted to the teeth as they go past and so closes a switch.

 

Thanks

I think you will find the coild is fed with an ac signal and it as the teeth pass the sensor it loads up the supplied AC to a greater or lesser degree. The ECU detects this change and can then deal with wheel rotation etc.

The same signal can be used to detect tyre problems as well, I made a unit top fit on my scorpio that used this information and could detect under / over inflated tyre's, punctures etc all before things got serious. The system relied on the effective diameter of the wheel changing and hence the ABS speeds would change.

 

Regards - John

[sad_git]

Abs sensors generate their own ac voltage of at least 0.2v up to .5v if the wheel is rotated at 60rpm. If your multimeter measures ac voltage it is a good check for faulty sensors.