dezzyd75

Hi,
Just before Christmas the ESP and ABS warnings lit up on the Mrs ML320. I read the codes which showed a fault with the front right speed sensor, ordering a replacement that i fitted yesterday. Cleared the stored codes, went to take it for a test drive and immediately got the error codes/ lights again.
Had a look online and found all sorts of info stating everything from faulty replacement part (non MB item..) to ABS control module so today swapped the one from the nearside, putting the one i removed yesterday in its place - cleared the codes again, drove off and..... exactly the same.
Using the diagnostic (iCarsoft i980) i checked the actual values and can clearly see the offside sensor isn't reading so my question is - is it likely to be the wheel bearing i need to replace as the tone ring is integrated? Also, has anyone had a similar issue or any luck with cleaning one of these?
Any info will be much appreciated

chassis

Is it possible to inspect the tone ring? If the tone ring is integral and not exposed to the elements, it is unlikely to fail. Using iCarsoft can you get any kind of reading on the newly replaced sensor, when removed from the suspension upright? I would try to affirmatively rule in or rule out sensor function. Also check the harness connectors for debris, corrosion, broken parts, etc.

dezzyd75

Hi Chassis.
Difficult to see anything through the hole where the sensor fits, its fairly well recessed and the tone ring (for want of a better way to describe it) is just a part of the bearing. in fact, looking at pictures online it just looks like a standard wheel bearing which i understand is magnetic on one side so you have to be careful to fit them the right way round. I've read threads where people have changed a bearing only to find the ABS faults - turns out to be the bearing fitted backwards.
I've put a multi meter across both both original sensors and also the replacement and get a reading of around 0.39 - 0.40 from each. I did a bit more research last night and think the next step is to try taking a reading while rotating the wheel.
With the scanner i've read the actual readings while the car is moving - stationary all 4 wheels read 0.69 (not sure why they read anything when standing still), once you start to move all values climb in line with the speed you're moving except the front right.
I'm confident to be able to rule out the sensor as i've fitted the 'faulty' one from the front right to the front left and its now reading normally so it can't be the actual sensor itself.
My thoughts are that maybe the bearing case is corroding, to be fair the car now has 130k on the clock so its possible. I changed the front left bearing around 12 months ago as it was noisy (no sign of play though), problem is we've since moved home and i no longer have a garage or drive to work from.

chassis

If you confirm all 4 sensors give the proper reading, then the problem isn't the sensors. Do you agree?

If the bearing is bad, but the sensor is good, you would not get the error that you are getting, Do you agree?

What else is in the electronic daisy chain, after the sensor?

flyboyusa

Did you ever find a solution to this dilema? I'm having a very similar issue with a ABS speed sensor. I've replaced the sensor, which fixed the problem for a couple months, now it's back.
I'm beginning to think it's either the wheel bearing magnetic ring -or- there's a wiring break/short somewhere.
Scratching my head!

Does anyone have the procedure to test the actual wheel sensor with a multimeter? I've seen numerous methods using resistance (ohms) -vs- AC voltage -vs- DC voltage.

Maj. Dundee

Please update your profile to include the year and model, is it gas, CDI or Blue and the country you live in.

dezzyd75

Fortunately, yes. Turned out to be the tone ring so basically a new wheel bearing cured it, seems to be a common problem.
Had a similar fault on a W204, luckily just a sensor to fix that one though.

expl0rer

Unless the tone ring becomes dirty in some way, it should not be a problem. Like it has been mentioned earlier, it is part of the bearing. The bearing is sealed on the "out" side, but on the "in" side you could actually see the tone ring if you are looking at the bearing from the correct angle and with light hitting the ring the "just right way". I had to replace a rear sensor of my X164. It was seized really well and in the process of removing it I am sure some plastic bits contaminated my tone ring. I have to replace the bearing.

I've noticed on mine that if your sensor is not working, the car will tend to brake hard from the starting line (experienced this when I had a bad front sensor). If the tone ring is the problem, I do not experience hard braking. The ABS and yellow triangle (ESP) illuminate on the dash. The car throws a code to clean or replace the tone ring. Code is observed with MBII scanner in the ESP page/module.

jg_civ

In my case, I had to replace 3 speed sensors and the ABS/ESP lights went off !!! I noticed that all the ones I pulled were corroded. As soon as I got done installed the last one, I turned on the car and starting driving off and everything dissapeared. That was my experience. Found out that it had something to do with my daughter being at the beach all summer with the SUV (ML350). Figured it was the salt water and sand that corroded them up. Plus living in Houston doesn't help! Its always very hot down here. I will say that the scanner did pop all three sensors...so I would say run a code scanner again and see what the ABS system is reading.

FONZYMB

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just curious is to how did you navigate the i980 tofind out which sensor is bad?

dezzyd75

Been a while since i used one (sold it over a year back) and replaced with a Snap On to cover other vehicles but from memory there's an option to view live data somewhere. You can check all sorts e.g. air and oil temp, exhaust gas temp, parking sensor data etc. - really handy to diagnose faults. Give me a shout if struggling, i may still have a manual for it somewhere