When driving on an icy road near my house, I noticed a peculiar phenomenon. Being a very new BMW owner (I've had my 2004 325xi for all of two months now) I decided to turn to the forums for some advice.

When I brake hard on an icy surface, I hear a noise coming from the front that I can only describe as "light grinding", accompanied by a small of vibration in the pedal.

What makes this interesting is that it only happens during heavy braking on ice or ice-like snow. I cannot duplicate the effect on dry roads or even rainy/wet roads. It also only happens when I'm using a fair amount of pressure, i.e. "slamming on the brakes". If I'm braking slowly and steadily, it doesn't happen.

Any thoughts?

That is your ABS (anti-lock braking system) responding. the system will not allow the wheels to lockup in any instance during braking - even on dry roads, which by the way, is harder to produce because of the higher speed and braking that is required to meet the criteria for the ABS to engage.

On icy/snow packed roads it is very easy to engage the ABS. You will feel in the brake pedal - kind of a hammering effect (engaging and dis-engaging).

That is your ABS (anti-lock braking system) responding. the system will not allow the wheels to lockup in any instance during braking - even on dry roads, which by the way, is harder to produce because of the higher speed and braking that is required to meet the criteria for the ABS to engage.

On icy/snow packed roads it is very easy to engage the ABS. You will feel in the brake pedal - kind of a hammering effect (engaging and dis-engaging).

What he said.

And this is not only in a BMW, this happens in all cars with ABS (to a different extent though). I can't imagine this is your first car with ABS!

Yup, definitely ABS. My bimmer is the first car I've owned with ABS... threw me off the first time I felt it - it was like having gravel on my rotors. For some reason other cars I've driven in the past that had ABS, didn't feel like this one does.

Thanks for the (very fast!) replies. This is actually only my second car with ABS, despite having owned about ten cars and a handful of motorcycles in my life. I wasn't incredibly worried, I figured it was just the ABS kicking in- after all there are no warning lights/no codes on my Peake tool. But while my Volvo's ABS had a little peddle vibration, it didn't make the same noise, and so I was curious if there might have been a problem with the ABS. Perhaps I should've just asked if the noise was normal for ABS.

At any rate, thanks again for the comments!!!

Thanks for the (very fast!) replies. This is actually only my second car with ABS, despite having owned about ten cars and a handful of motorcycles in my life. I wasn't incredibly worried, I figured it was just the ABS kicking in- after all there are no warning lights/no codes on my Peake tool. But while my Volvo's ABS had a little peddle vibration, it didn't make the same noise, and so I was curious if there might have been a problem with the ABS. Perhaps I should've just asked if the noise was normal for ABS.

At any rate, thanks again for the comments!!!

Don't feel bad. Different cars have different feedback.
You asked the question in the right place and got good answers.:buttrock
My xi's ABS feedback seemed excessive when I firs t felt it, but now it is a comforting feeling. Play in a snow covered lot with DSC on and off and get used to it. It is a powerful system. With good tires on all corners my car is very predictable, but it has limitations. Learn what they are and have fun, but be safe.

E46 ABS does seem a little aggressive. When I first experienced it, it seemed a little more pulsing and overall unpleasant than other cars. The pedal noticeably seems to sink in more during ABS. But these things are tuned for response, not for feel.

Don't feel bad. Different cars have different feedback.
You asked the question in the right place and got good answers.
My xi's ABS feedback seemed excessive when I firs t felt it, but now it is a comforting feeling. Play in a snow covered lot with DSC on and off and get used to it. It is a powerful system. With good tires on all corners my car is very predictable, but it has limitations. Learn what they are and have fun, but be safe.

One of my favourite pastimes is to take the new ride out for a "spin" on a nice icy lot.


Thanks again for all the great responses!

E46 ABS does seem a little aggressive. When I first experienced it, it seemed a little more pulsing and overall unpleasant than other cars. The pedal noticeably seems to sink in more during ABS. But these things are tuned for response, not for feel.
+1