CharlyE500

I am not sure what's wrong... everything is fine and all the sudden when I brake (not too hard) but the car gave me a heart attack brake. It brake so hard my face hurt ! I did not brake very hard, maybe only 40% of it... this happen 3 times already in about 3 months. It was really scary !
Anybody has any idea that what possible make this ? wrong brake parts ? bad brake fluid ? Thanks for any advise.

shadenfroh

Could it be that your Brake Assist activates prematurely? I've felt BAS a few times when I got carried away. I slammed the brakes to the point where ABS just barely engaged and suddenly I felt the brakes bite really hard, without me pressing further. And yes, the full braking power of these cars is enough to throw you out the windshield.

Here's a quote from wikipedia on BAS operation:

"By interpreting the speed and force with which the brake pedal is pushed, the system detects if the driver is trying to execute an emergency stop, and if the brake pedal is not fully applied, the system overrides and fully applies the brakes until the Anti-lock Braking System (ABS) takes over to stop the wheels locking up."

I doubt that pads or fluid are the cause. The brake light switch sounds like a possible culprit, but I'm just guessing here.

CharlyE500

In my previous E55 I had brake light switch problem and the ABS/ESP dash light was ON. But my current car has no light on at all. Let me change the brake light switch if helps. Any other possibility ?

shadenfroh

I normally don't throw parts at problems, but I would change the switch, since it's cheap and easy. If it fixes your problem, cool. If it doesn't you can throw the extra switch in the trunk for when it inevitably fails. I carry a brand new one in the car.

Then I would drive to a shop first thing in the morning. I don't fool around with brakes ever.

Edit: By no light at all what do you mean - the bulbs don't even light up with the key in position 2? I guess you could have a sensor or switch that's sending corrupted data without throwing a code.

CharlyE500

What I mean no light is no warning light in the dash. If the brake switch has problem, the BAS light should be On in the dash like my previous E55.
This one just no error message but the brake is scary. It bite so hard without pressing hard the brake.

shadenfroh

I understand. That's why I said:

And it might not be the brake light switch at all, I couldn't find that much info on how BAS works. I'm just speculating here, but seems to me that data is being sent, but it's crap data. Hence no error and untimely functioning system.

cm60k

Don't think brake switch do this..!,

i might be wrong; but assuming;

spring armature in M/C went bad, due to the age, it's closed hardly when press the pedal,,

oil pressure will be differ, and that will interrupt the signal in the ESP pump through speed sensors..!!

"ZAYED"

CharlyE500

In this case, what should I check first ? Speed sensor ? how can I check oil pressure ? Thanks !