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-   -   X-3 ABS system (http://www.bimmerfest.com/forums/showthread.php?t=702983)

longhornfan 06-14-2013 03:57 PM

X-3 ABS system
 
I am wondering if anyone else has had trouble with the ABS system initiating under ordinary braking, weather and road conditions. I have had two instances where I was routinely braking and the system has kicked in. Yesterday, everything locked up as I slowed for a red light and I lurched forward at a light and hit the rear of the car in front of me. BMW service says everything checks out fine and there are no fault messages. They claim there was something about the road condition that caused this.

grebersole 06-14-2013 04:42 PM

X-3 ABS system
 
What year and model is your vehicle?


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The X Men 06-14-2013 05:00 PM

I don't understand, how did the ABS make you lurch forward?

longhornfan 06-14-2013 05:09 PM

X-3 ABS system
 
I have a 2013 X3
I can only tell you what it felt like and what the dealership attributed it to since I am not very familiar with how the ABS works. It felt as if my brakes locked up and then it felt like a pumping sensation that caused the car lurch forward. I was simply braking for a red light in dry conditions. Dealership said it sounded like I was describing how the ABS system would react to slick pavement to keep from skidding .

aberrant 06-14-2013 06:33 PM

X-3 ABS system
 
Are you sure it wasn't the drag produced by the dynamic charge system? That comes on at slow speeds and produces very noticeable engine drag. I don't know that I'd describe it as 'lurching forward' though.



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Drewsky 06-15-2013 05:12 AM

A couple armchair-quarterbacking notes:

-you said the system "locked up". ABS never locks the wheels. When abs engages, it is QUITE noticeable: you feel it in the brake pedal and you may hear/feel a pulsing "shudder" throughout the vehicle.

-you didn't say how fast you were going or how hard you were braking. As other posters have commented, the engine does a good deal of "engine braking" and it is very evident when very gently slowing. When the vehicle downshifts it can feel like a decrease in braking. If this resulted in a collision you are following way too close to the car in front of you!

-The human body isn't very good at interpreting changes in the change of momentum. For example, a change from a "hard stopping" deceleration to a "gentle stop" deceleration can actually FEEL like an acceleration. Thus your "lurch foward" you felt was most likely a change in the slowing speed.

-Hitting a slick spot will decrease overall braking to the wheels slightly. As mentioned above, this decrease in braking can feel like an acceleration. (fun fact: engaging ABS on a motorcycle *REALLY* makes this feel evident!! It is quite a strange feeling)

The X Men 06-15-2013 05:23 AM

I agree, the ABS should not lock the brakes, in fact, it is a anti lock system to prevent locking. Sounds more like a braking problem to me, the brake froze somehow and then let go altogether causing the lurch forward.

Liverman 06-15-2013 09:45 AM

Quote:

Originally Posted by The X Men (Post 7652764)
I agree, the ABS should not lock the brakes, in fact, it is a anti lock system to prevent locking. Sounds more like a braking problem to me, the brake froze somehow and then let go altogether causing the lurch forward.

As aberrent stated - that is the dynamic charge or energy regeneration system. You'll see it's action in the display under the tach. It is automatically turned on and off by the car's computer. I do not know the parameters used by the computer to decide when to engage and disengage, but it appears (based on my 3000 mi driving experience) to be when coasting or braking.

When it is engaged, there is a noticeable drag. When it releases the sensation is the car lurching forward since drag is reduced. I have only noticed the drag/release when I am coasting or have the brake only very lightly engaged.

From your description, it sounds like it is working as designed.

But maybe I don't understand - when you say "everything locked up" and "brake froze" did the wheels lock and result in screeching tires and marks on the pavement?

poker838 06-16-2013 07:24 AM

Gents, there is no Hybrid-style brake energy capture on this BMW. It is purely a marketing spin. We only get a trick alternator that only charges when you're off throttle. It is not connected to the brake system and should not provide any meaningful deceleration

The X Men 06-16-2013 07:31 AM

Quote:

Originally Posted by poker838 (Post 7654447)
Gents, there is no Hybrid-style brake energy capture on this BMW. It is purely a marketing spin. We only get a trick alternator that only charges when you're off throttle. It is not connected to the brake pedal.

I agree, Its not like the engine is being drag down by a huge drive motor as in a hybrid. The BMW regenerative system is just a normal size alternator dragging the engine, which does not amount to much drag.

longhornfan 08-19-2013 02:15 PM

After my post, I had a second incident which allows me to describe a little better. I was slowing for a red light and I could tell that I was not getting full power in the brakes, followed by a surge of acceleration. Had there been any oncoming traffic, I would have sailed into the intersection. As it was i was able to make a turn at the corner and stop just outside the intersection. Engineer for BMW of North America has inspected and can't identify a problem.

Drewsky 08-19-2013 05:08 PM

Quote:

Originally Posted by longhornfan (Post 7783120)
After my post, I had a second incident which allows me to describe a little better. I was slowing for a red light and I could tell that I was not getting full power in the brakes, followed by a surge of acceleration. Had there been any oncoming traffic, I would have sailed into the intersection. As it was i was able to make a turn at the corner and stop just outside the intersection. Engineer for BMW of North America has inspected and can't identify a problem.

I reread all of your posts. This one makes as much sense as the rest of them. First you say the brakes lock up, now you say that they aren't doing anything.

It sounds to me like the problem is a faulty driver module located behind the steering wheel. Replace that and the problems will clear right up. :thumbup:


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