ABS Kicking in - Possible ABS fault?

[chrisguttridge]

Hi All,

need some help if I may. My rear hubs need changing due to the bearings making an awful sound. So I got all the parts and the day before I changed them I found that I had limited breaking. When I was breaking at low speed the abs was kicking in. However there is no ABS warning light coming on. So I suspected that one of the ABS rings had cracked on the rear hubs. So I changed the rear hubs yet the problem persists.

Interestingly when the ABS kicks in at low speed I get no warning lights or anything.

So to test it I disconnected the ABS on the drivers side front and now obviously get the ABS warning light with the service light on but I dont have any issues under breaking.

Any ideas what this could be?

Any help would be appreciated

[davelowe]

Rear discs usually come with the ABS ring incorporated. Check they are present. The ABS does not function at low speed by design.

[chrisguttridge]

thanks dave but as I mentioned on my original post the issue was present before the rear hubs were changed...

I ensured I purchased the correct rear discs which came with the abs incorporated into them

Any ideas?

[FOOTBALLGETTO]

Hi,

Could you have dirt on a sensor?

Just a thought. If you had a duff sensor then you would get an ABS caption but wondering if some grit or grime could give you your symptoms at low speeds.

Regards

Tony

[davelowe]

If I remember correctly, the sensor is magnetic, and can so be fouled by iron particles on its surface. The above post is highly relevant. Remove them and inspect.

Let us know how you get on.

[chrisguttridge]

Hi both,

Apologies for the late response. I have checked all abs sensors and they are all clean. I gave them a good clean before I put them back in place. Still no joy - Shall I admit defeat? Take it too a garage...

[davelowe]

My last thought is that the sensor(s) were damaged by actually hitting the reluctor rings - assuming the bearings were really bad. The tolerance is very tight.

Off the top of my head, I can't think of a way to test them aside from using an oscilloscope.

[tomalamix]

when the ABS goes in action you will not have any light on the dash, it only lits if there is a problem with your abs system.

diid you check the rear brake pads? arent they too much worn and are getting against the brake discs?

[MicKPM]

Plug it in and see what the ABS management is seeing to trigger the system... Guess work is frustrating and pricey!

Mick

[davelowe]

Plug it in and see what the ABS management is seeing to trigger the system... Guess work is frustrating and pricey!

Mick

This is good advice. One can trigger the ABS using CLIP deliberately to purge it of air. I don't know of any other diagnostics that will give you as much detail. OBD will not (is that a complete sentence?)

[chrisguttridge]

so the rear discs and pads were new, I had this problem before i replaced the rear pads discs/ i suspected the abs was kicking in due to the rear bearings hence why i replaced the rear discs. Its still an issue however i currently have the abs plug unplugged and the brakes are working fine, obviously the abs isnt working i assume. As the abs is unplugged i have the abs light and service light lit on the dash.

Any thoughts on next steps?

[AlexB]

Some aftermarket ABS rings may cause this problem...

[chrisguttridge]

i dont see how the new rear discs/pads would cause the issue. Just to point out the issue was there before i changed the rear discs so it has got to be something on the front end

[chrisguttridge]

Do we think there could be a crack in one of the front reluctor rings? I'm going t have a look tomorrow when I can jack the car up to see if there are any cracks.

Do you think it's worth a shout?

[AlexB]

Please read this for general information. Our sensors are active, Hall effect type. These are the most advanced in terms of performance. The plate around a sensor usually gets corroded and can be deformed. Pull the sensor out, remove all rust, remove any metal shavings (remember your failed bearings?!!) that can be masking the magnetic field, apply anti-corrosion paint to the metal, make sure the distance between the sensor and the ring is correct. This is the mechanical stuff. The next is to check the electronics. This is as usual: ground, power, signal, condition of wires... The Hall effect sensors fail internally occasionally. If one of them is dead or starts to "miss" pulses, then replace it. Still, I think the problem might be mechanical, as the ECU does not detect the problem.

These sensors do work at low speeds. The ones that did not work were the old passive type sensors, because the strength of their signal was proportional to the speed of rotation.

https://www.ukpartsdirect.com/faqs/faqs- ... bs-sensors