ABS sensor keeps failing

[mw52563]

Hi
Hoping someone can help... I recently installed a new speed sensor (front passenger) on a 2011 infiniti M30D. I had to drill the old one out so its in bits. Only problem is I'm still getting an ABS sensor error. If I clear the codes using an OBD2 then the light stays off for about 100 metres then comes back on. What ive noticed is if I choose live data on the OBD2 all the speed sensors give roughly the same speed, including the front passenger. But for some reason it will randomly drop from say 40MPH to 25MPH only for a split second but that seems to be enough to cause the error. Anyone have any ideas why its doing this, like i said i did drill the old one out so could it be that Ive damaged the hub
Thanks for any help
Mike

 

[Burnerman]

Just wondering if you've damaged the reluctor toothed wheel, when you drilled the sensor out? One tooth damage is all it needs
Te ABS system only works after a few MPH which could be why you get the 100m delay.
John

 

[rsgaz]

some reason it will randomly drop

Could be a fault (internal fracture) with the cable to the sensor rather than the sensor. They get continually flexed, the rears, only up and down, the fronts, of course, a lot more. Eventually it breaks the copper inside the wire, but the PVC holds together, mostly keeping the broken copper ends touching, thus giving an intermittent fault.

 

[mw52563]

Just took the wheel off to have another look and I think I've damaged the reluctor toothed wheel by the looks of it.. do you know if you can just replace the toothed part or does the entire hub have to be replaced?

 

[Burnerman]

Sadly I only have experience with Renault hubs, and in those the bearing and ring come as one Sorry I can't help with the Infiniti but it does look similar!
John

 

[leegsi]

Thats definitely the prolem

 

[Burnerman]

Yes, I’d certainly agree there.
John

 

[Gasguru]

4.52 shows the encoding ring...

 

[mointainwalker]

This is just theory and speculation because I can't see the breakdown of parts, but if you've got the time and inclination, you may find it of interest.

I used to work for a magnet company that was one of only two to supply the European automotive industry : Q1, TS 16949 and all that. Amongst the parts we made - 20 years ago - were 58 pole ABS sensor-ring plastic-magnets:; personally I wasn't selling these but they did get discussed in technical-meetings/sales-office etc, so I have some knowledge.

These magnets would be only 1 mm thick and would normally be in front of a toothed-ring so that the sensor could see on/off/on and compare that speed with other wheels to activate the ABS. The photos shown here by mw52563 depict either a cast-iron or cast-steel ring with a drill groove in it. Neither cast-iron nor cast-steel is a permanent- magnetic material, although they are both soft-magnetic materials - i.e. they exhibit magnetic properties when they are under the influence of a permanent-magnet, but lose these when the permanent magnet is removed. Logically this has to mean that the permanent-magnet is behind the ring (trying to cast it into the ring would destroy it).

If the damaged components new are expensive to replace - and I would expect them to be very expensive because of uniqueness - then you might consider repairing this ring. Since it is only transmitting the magnetic-field ( as I see it ) , you could weld and machine the ring to give it its original dimensions and it might work.

I have to emphasise might because magnetic-fields are very sensitive to varying material-density and this is certain to be altered by welding/machining: depending on the chosen sensitivity of the sensor, this might well still deliver a fail. If I haven't been sufficiently clear on anything, please ask and I will try to do better.

Personally I would check out all the connecting-looms first to see if a wire hasn't fractured ( as suggested above ) due to excessive movement when you were removing/replacing components.

 

[Burnerman]

Interesting post, mointain!
I have noticed when I need new wheel bearings which incorporate the ABS ring sensor they only seem to come complete with the hub - or in Renaults case with the disc too.
I guess this is to minimise any chance of damage to the sensor - bearing presses aren't renowned for finesse so there's a high chance that mechanics would damage it.
John

 

[Gasguru]

All this tech and added complexity...but ABS has very little effect on accidents.
So many idiots either don't press the brake sufficiently hard, forget to steer round the obsticle or drive like idiots thinking the system will enable them to stop on a sixpence.
Surviving crashes takes experience
If the money was instead spent on better driving standards....