[pault949]

Recently, my 2014 BMW X3 xDrive28i has been automatically braking in the rain.

When driving down the highway at a constant speed in the rain (moderate to heavy) the vehicle will intermittently hit the brakes and slow down nearly 10 mph until it decides to let off the brakes. This is all without changing the throttle position or any standing water around (I am 100% certain this isn't a hydroplaning issue).

Another issue that I have noticed recently even in the dry, is that sometimes when I am at low speeds and hit the brakes lightly, it feels like it's hitting the brakes a lot more than the input that I am giving. I will then let off the brakes and it still feels that the brakes are lightly engaged because it will eventually come to a complete stop and sit there stopped with my foot not on the brakes (it should be idling forward at this point).

The brakes are newer with the rears being changed just over a year ago and the fronts being changed just under a year ago. I have driven several times in the rain after the brakes being changed but haven't noticed this issue until just recently therefore, I don't think it's the pads or rotors; it feels like there's something wrong with the electronics.

If anyone knows, please advise.

Thanks in advance.

[pault949]

Alright, cruising on other forums around the Internet, I found this thread: https://www.pistonheads.com/gassing/...f=72&t=1605022

This gentleman describes exactly what I had described above and he mentioned that BMW diagnosed it as a 'failed DSC hydro unit'.

Anyone have any experience with that?

[spucktacular]

Greetings,

I would have to agree with your findings. If you analyze the facts systematically, the hydro DXC is probably the only component able to cause the symptoms you describe.

1) your 2014 doesn't have any emergency braking system does it?

2) if you were having mechanically faulty callipers, potentially on the verge of seizing up, you'd probably notice pull to one side or another.

3) the only component in your car able to alter the braking dynamics electronically is the hydro DXC unit.. if I were you I'd have that taken care of quick.

My personal advise, get that fixed quickly and properly by a BMW dealer. The main component able to modulate brake line pressure is inherently so critical to your personal well being, that it's simply not an option to DIY it. If its electronic circuitry, you can't fix it.. if its a mechanical/hydraulic problem within the unit, again you can't fit it yourself. Even a dealer can't service it, they'll swap the whole unit.

I've noticed the official bmw parts catalog shows a few revisions to that part, meaning theres definitely something they realized could be improved. Bad news is it will cost you if you don't have warranty, good news is you'll probably get it replaced with the latest version.. meaning you won't have to worry about it again, and probably have better brake feel.

http://www.realoem.com/bmw/enUS/show...diagId=34_1933

Do you want to risk loosing your brakes fully if that thing completely short circuits and goes dark? honestly at any speed it's gonna be an accident, but at high speed it might be your life.

good luck, and don't put your kids in the backseat till you sort that out..

Originally Posted by pault949

Alright, cruising on other forums around the Internet, I found this thread: https://www.pistonheads.com/gassing/...f=72&t=1605022

This gentleman describes exactly what I had described above and he mentioned that BMW diagnosed it as a 'failed DSC hydro unit'.

Anyone have any experience with that?

[pault949]

spucktacular

Thanks so much for that reply. I completely agree with you on the safety issues this causes. In fact, as I was driving in to work this morning it was raining and it applied the brakes by itself on four occasions. I was feeling experimental and decided to disengage the auto-wipers (turned off wipers completely) and it didn't do it any more. From other threads that I have been reading, the auto-wiper utilities enables the disc drying feature.

Let me answer your questions:
1) No, my vehicle is not equipped with the emergency braking system.
2) I am not feeling any pull to one side or another during the 'auto braking' issue nor during regular braking.
3) I have an appointment early next week to take it in to the dealer, but I am thinking about taking it in earlier.

When I talked to the dealer, they mentioned that it would be hard for them to reproduce the issue because it only happens in the rain. I would like them to at least check for moisture in the brake reservoir because that would be a good indicator that this is the issue. Not sure if they can check the DSC hydro unit as well (not sure there are diagnostic tests for it).

This will be addressed ASAP. For the time being, I will not be transporting my family in this vehicle until all this is sorted out. I have a couple months left in my CPO warranty, but I am not sure that this issue would be covered.

[Opie55]

That should be covered for sure. If you don't have the copy they gave you when you bought the car, Google for BMW CPO coverage or exclusions and you'll find a one page BMW document that lists what is not covered. It's a long list, but it's mostly normal wear items - upholstery except seat heaters, trim, suspension parts, certain transmission parts, glass except electronic parts (defrosters), etc. You should print it out and read it. Take it with you to the dealer.

[pault949]

Opie55

Thanks for that tip. I shall find it and print it out for the dealer visit.

I am sure hoping that it's covered as it doesn't look like a cheap part at all.

[spucktacular]

Safety First

Originally Posted by pault949

spucktacular

Thanks so much for that reply. I completely agree with you on the safety issues this causes. In fact, as I was driving in to work this morning it was raining and it applied the brakes by itself on four occasions. I was feeling experimental and decided to disengage the auto-wipers (turned off wipers completely) and it didn't do it any more. From other threads that I have been reading, the auto-wiper utilities enables the disc drying feature.

Let me answer your questions:
1) No, my vehicle is not equipped with the emergency braking system.
2) I am not feeling any pull to one side or another during the 'auto braking' issue nor during regular braking.
3) I have an appointment early next week to take it in to the dealer, but I am thinking about taking it in earlier.

When I talked to the dealer, they mentioned that it would be hard for them to reproduce the issue because it only happens in the rain. I would like them to at least check for moisture in the brake reservoir because that would be a good indicator that this is the issue. Not sure if they can check the DSC hydro unit as well (not sure there are diagnostic tests for it).

This will be addressed ASAP. For the time being, I will not be transporting my family in this vehicle until all this is sorted out. I have a couple months left in my CPO warranty, but I am not sure that this issue would be covered.

[Bgroff28]

Pault949

Did you fix the self braking issue? I’m having the exact same problem. I recently bought my car, 2014 M235i, took it to bmw and they said the cause is most likely from the aftermarket pads and rotors and did not see anything wrong with the DSC Hydro unit. So I am waiting for new bmw pads and rotors to get here, hopefully that will fix it, but we shall see.

Thanks