Brake fault on 210

[R W]

I have not been on here for a while but would appreciate some help. My 2001 210 has a function where it senses an urgent application of the brakes and assists the braking. Sometimes while driving or slight brake pedal application it feels like the system is braking the O/S/F wheel only, for no reason. It flashes the orange triangle and puts on ABS/BAS lights. When the car comes to a stop it seems to reset its self ad drive normally. It can do this randomly while driving but twice it has done it when light brake pressure is applied to just slow dow. It does not show any pattern to it activating. We have checked fault codes and no codes showing.
Is it possible for this system to brake only one wheel as its function is to brake the car faster in an emergency. if anyone can advise or shed any light on the problem I would appreciate it.

 

[brandwooddixon]

If I remember rightly the W210 has a brake booster for emergency braking, which I think is applied to all circuits and thus would effect more than just the one wheel.

Could the issue actually be a triggering of the ABS on a wheel instead?

The W210 doesn't have a separate reluctor ring for the ABS sensor, but instead has notches machined into the hub itself. These rust over time and can cause issues for the ABS. I recall having to replace the front hubs of my W210 for just this reason.

The notches are visible without needing to remove the hub. If they look pretty rusty you could try cleaning them up, in case this has a beneficial effect.

 

[R W]

brandwooddixon​

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Thank you for your reply. Yes you are right the brake boost does apply to the whole system and not just one wheel. I dont understand why it would activate the brake on one wheel only. But it is scary when it happens and dangerous if another car is behind me. No warning at all it just suddenly brakes
I may be wrong but would the ABS system only stop/control heavy braking in the event of a wheel skiding. Not put a brake on?
My problem is the brake seems to be applied so violently its almost to the point of skiding

 

[LostKiwi]

Sounds like ESP is thinking a wheel is spinning and trying to control it by using the brakes. I'd be looking closely at the wheel speed (ABS) sensor. You could try turning ESP off to see if it still does it.

 

[Frontstep]

As above, clean it up first.

 

[R W]

Thank you for your advice. I will clean the ABS sensor and try it and try it with ESP off if its not cured.

 

[mersum1es]

Yes, reluctor ring can be rusted off and spinning reely/jamming occasially. There is no codes because car thinks its normal.

 

[brandwooddixon]

Inspect the hub, inboard face it has the notches machined into it for the ABS sensor.
If I remember rightly I bought new front hubs that came with bearings already fitted.

 

[alexanderfoti]

As above!! Check actual values for wheel speeds on diagnostics whilst driving, but NSF is probably the one with an issue.