Another ABS sensor gone!

[robert_e_smart]

It was a long time a go now. But I think the light was off permanently. It would lock up and skid as if it had no abs . Trials with resistors pass the static test then the light comes on after a short drive.

[CitroJim]

Now that's interesting Robert. Definitely worth repeating with an ELIT on a live test to see what was going on there...

The amplitude of the sensor signal must have been rather different or something...

[kenhall]

I bought a couple of these relatively cheap VAG ABS sensors a while back as potential insurance for replacing possible future non available Teves sensors. The thing that strikes me about them is that whilst they match the Teves sensor resistance wise the magnetic pole separation distance differs slightly. Presumably this distance is matched originally to the reluctor tooth dimension / spacing. Would this have a possible effect on the purity of the AC signal waveform generated by the sensor when used with an XM reluctor? An experiment with an oscilloscope connected would be revealing.
I would go along with RobertM's suggestion that replacing the sensors one axle or all four sensors at a time will probably be necessary.

Ken

[xmexclusive]

The ABS start uptest is simply of resistance value.
Substituting using a correct value resistor works fine for the start up test.
Substitute with resistors on all 4 wire pairs keeps the light out when moving as the ABS thinks the car is still stationary.
While there is no brake application the ABS moving vehicle test looks repeatedly at the sensor wave form counting the frequency of the oscillations.
It expects to see the same frequency from each sensor on an axle.
Tolerance limits are very tight so substituting with non standard sensors requires waveform shape and magnitude checks.
I think substituting a pair of non standard sensors on a single axle is unlikely to help much.
This is because the ABS ECU does an even more complex front to rear sensor check as well as the cross axle one.
Because of these limitations I suspect that in car testing of alternatives is unlikely to find a good solution.
I have looked at making up a variable speed motor driven test rig for comparing alternative sensors.
My first idea was of a single driven ring with 4 sensors at the quarter points.
This was rejected when I realised that the XM has 48 tooth rings at the front and 29 tooth rings at the rear.
A difference the ABS ECU is programmed to check for.
So the test rig needs two seperate rings sufficiently apart for the sensor magnetic fields not to interfere with each other.

John

[citroenxm]

Front and rear sensors are all identical shape and mounting wise .. so what would happen if a front sensor was fitted to the rear? or is that irrelevant because the Ecu takes accounts of the different teeth rings and not the actual sensor???

[xmexclusive]

Hi Paul

Have just edited in to confirm your thoughts.
The sensor moulded mounting position is critical to get the coil signals right.
The soft iron centre core of the sensor also has to be correctly orintated to the ring teeth.
You have got me thinking and I realised there is a third type of ABS system (Bosch 2SE) with sensors that physically fit the XM.
Those were used on the Pug 605.
That Bosch ABS system is in much more common use so very cheap.
Must try to obtain a sample one to examine and compare.

John

[casalingua]

I´ll be watching this thread with interest. I am impressed at the level of techical competence being displayed.

[robertmnorton]

Hi John, Teves equipped cars, at least my S2 Mk20E system, has a 48 tooth rotor at the rear, same as the front.
robertm

[casalingua]

This firm is stepping into the gap to remake out-of-production parts. Alas, the XM/Bendix ABS system is not one of them.
http://www.bba-reman.com/HintsAndTipsNavigator.aspx
But what´s this? Is this a help?
http://www.bba-reman.com/content.aspx?c ... abs_system

[kenhall]

Hi John, Mister Auto has ATE sensors available with 35% discount at £37 for the rear with discount applied.
robertm

Thanks for the tip Robert! I bought a front Teves sensor from Mister Auto for £29.50 delivered. In my experience these sensors lead the hardest life and my failures have been due to them going open circuit.
Interesting info on the box - ATE Teves (founder Alfred TEves) was taken over by Continental Aftermarket GMBH in 1998 and the sensor was made in the PRC (what isn't these days!)
Checked the barcode OK on the box (as suggested to confirm authenticity) at www.ate.de. Parts catalogue available on this website.

Ken