Technical ABS Sensors - Drum Brakes

[dado1975]

Hey all,

Been getting the ABS warning at start up (comes on before engine starts - stays on) so took the rear drums off to have a look at the sensors yesterday.

From other threads here i was expecting to see a toothed ring under the sensor which i did. However, as soon as i touched it all the teeth just rubbed off like they were made of powder. With just a little rub of the finger this ring became completely smooth all the way round.

So on further trawling previous threads i see there seems to be some debate whether this ring is supposed to smooth or toothed! It did seem to me that the teeth had to just be dirt deposits because they rubbed off so easily.

So i'm guessing it's supposed to be smooth then? Also, is it supposed to still have the rubber ring round it? There was talk on another thread of there being a shipping protection thing that should be removed or is that something else?

Any other thoughts on how to solve my ABS light problem? How exactly should i be cleaning these rings/sensors? MOT next month and money is too tight to mention. Any advice greatly appreciated.

 

[jwmultipla]

Hi,

Yes the sensors are 'smooth' I changed my rear wheel bearing recently and in the kit which was listed as ABS was what looked like and oil seal. when i took the drum off i saw what you saw which was what appeared to be a toothed ring but when i touched it all the teeth wiped off. I fit the new parts in the box and no ABS light came on so i can only assume that the 'teeth' are within the seal under the trubber and the teeth that you see are just bits of brake dust that are sticking to the seal. hope this helps

justin

 

[dado1975]

Thanks for the reply Justin. So i'm re-assured that the ring is supposed to be smooth and not so horribly degraded that it has disintegrated. That's good news at least!

Unfortunately that leaves me no further forward in terms of why the ABS lights is on just now.

Anybody got any other thoughts on diagnosing the ABS problem? As i understand it the diagnostic software available tells little about ABS faults so where else can i look? Any special way of cleaning the sensors? Anything else that is easy to check or clean?

 

[Greyhound_Shrops]

Hello,

Are you able to do diagnostics at home? If you are able to access the ECU it should tell you which of the sensors is the problem one. It doesn't give any specific details though.

Also, if you have not used diagnostic software, how do you know that the rear sensors are the ones at fault? There are sensors on the front hub carriers as well.

As a thought, you might want to check the cable of the front offside sensor. On my car, it had come adrift of it's clips and chafed through on one of the belt pulleys. I don't know whether this is a regular problem with Multis. I have made a temporary fix and cut out the affected section (about 1" long) and crimped the ends together.

In my case, I think I am going to have to replace the ABS ECU. This will be second hand since Fiat want over £800 for a new one.

Good luck.

Ian

 

[dado1975]

Hey Ian, thanks for the reply. Things have progressed but I wasn't sure of the correct etiquette round here, whether to bump my post with an update or let it quietly die off!

I suspected the rear sensors only on a hunch really, as the right/rear brake is making unhealthy noises it seemed like the likeliest candidate. I hadn't ignored the fronts before but was starting the in depth inspection at the back first.

Having seen nothing of note at the rear (and being reassured that the collar was supposed to be smooth and not toothed!) i re-inspected the fronts.

As it happens i found a nick in the driver side front sensor cable. It was really close to the sensor itself and i didn't notice it on my first pass. It hadn't severed the cable entirely so i suspect it was possibly there when i bought the car back in December 2010 (no ABS warning then of course) and has now just succumbed to corrosion????

Anyway, seems like i can get a replacement online for ~£25 or so. Hopefully that'll be all sorted when that comes. Seems like removing the old sensor is going to be the hard part, i already tried a bit without any joy but figured i'd wait til i had a replacement.

Expect to see my 'how to remove front ABS sensor?' thread sometime soon