[SmittydoughF30]

My car is putting on the brakes for me in the rain.

2014 328i 6MT, purchased in 2016, certified pre owned car.
35K miles on the odometer.

Summer is here in Florida and that means a solid thunderstorm every day in the afternoon for about 10 minutes.

When I am caught in one of these downpours the brakes will be applied for me. In traffic. ON THE FREEWAY. REPEATEDLY happened in the last downpour.

Details

1. Brakes are applied significantly but not pedal all the way to the floor.
2. I quickly lose 20-30 MPH then the car gives me back control.
3. In a bad downpour it happened so many times I learned to override it by quickly putting the accelerator to the floor.
4. This has occurred multiple times.
5. Cruise on and cruise off.
6. Both to me and when my dad borrowed it.
7. Surface streets and highway.
8. The windshield has 3M 70% ceramic but this happened both before and after installation.

Any thoughts or ideas?
Could the windshield tint have done this?

I have a service appointment scheduled for 3 days from now so any help would be appreciated.

[Eschmacher]

Originally Posted by SmittydoughF30

My car is putting on the brakes for me in the rain.

2014 328i 6MT, purchased in 2016, certified pre owned car.
35K miles on the odometer.

Summer is here in Florida and that means a solid thunderstorm every day in the afternoon for about 10 minutes.

When I am caught in one of these downpours the brakes will be applied for me. In traffic. ON THE FREEWAY. REPEATEDLY happened in the last downpour.

Details

1. Brakes are applied significantly but not pedal all the way to the floor.
2. I quickly lose 20-30 MPH then the car gives me back control.
3. In a bad downpour it happened so many times I learned to override it by quickly putting the accelerator to the floor.
4. This has occurred multiple times.
5. Cruise on and cruise off.
6. Both to me and when my dad borrowed it.
7. Surface streets and highway.
8. The windshield has 3M 70% ceramic but this happened both before and after installation.

Any thoughts or ideas?
Could the windshield tint have done this?

I have a service appointment scheduled for 3 days from now so any help would be appreciated.

Sounds like an issue with the emergency braking system, which I believe is fed by the camera in the rear view mirror. Do you hear beeping when this braking occurs?

Do you have your front end collision warning set to early by any chance? I have no idea if this actually changes the braking time, but it does change the warning time.

Edit: it also appears to use the adaptive cruise control radar pod.

[chowser51]

Check your brake fluid for moisture?

Have them code:
Ista.retrofit.brake wet. Low

maybe your brake drying feature is set to high.

[Rmcmac]

Son has a 2015 bmw 320i and he’s experiencing the brake drying feature anytime the wipers are on (rain or shine). Any ideas on a fix?

[SmittydoughF30]

Thanks to all for the input. A few clarifications.

There is no beeping during the intervention.
I do not have adaptive cruise control.
I can't find a setting for collision avoidance - I do not think I have that. I looked on the original sticker and nothing like that is listed.
I *have* noticed that brake drying is probably happening in dry weather.
Many thanks for the tip about brake fluid. I will have them look into that thoroughly.

I'll post another update after my service visit.

[cfm56d7b]

DSC will apply brakes under certain conditions. Did you try to disable DSC and see if the symptoms persist?

It's also worth learning if any codes have been stored.

Please post an update after the service visit.

[SmittydoughF30]

I disabled DSC and it did NOT happen again. However, the intense rain subsided before I made that change.

Service appt tomorrow- will update after that.

[thisismikeyb]

Since this only happens when you are driving while it is pouring out, are you sure you are not hydroplaning and the car is intervening to keep control? Also how much tread is left on your tires? Is your DSC light flashing while these events are happening?

To me it sounds like the car is determining that it is about to lose or it lost traction.

[cfm56d7b]

Originally Posted by SmittydoughF30

I disabled DSC and it did NOT happen again. However, the intense rain subsided before I made that change.

Service appt tomorrow- will update after that.

Thanks for the feedback. Please update this thread after the service visit.

[SmittydoughF30]

Originally Posted by chowser51

Check your brake fluid for moisture?

Have them code:
Ista.retrofit.brake wet. Low

maybe your brake drying feature is set to high.

Looks like chowser51 was spot on!

Drying was set to high. They set it to LOW and said that's all they found.
They kept it a couple days but it didn't rain while they had it.
So, they returned my car after changing that one line of code.

Also, they mentioned that if it does do it again, turn the auto wipers off. brake drying and auto wipers are controlled by the same sensor.

THANKS TO ALL.

[cfm56d7b]

Originally Posted by SmittydoughF30

Looks like chowser51 was spot on!

Drying was set to high. They set it to LOW and said that's all they found.
They kept it a couple days but it didn't rain while they had it.
So, they returned my car after changing that one line of code.

Also, they mentioned that if it does do it again, turn the auto wipers off. brake drying and auto wipers are controlled by the same sensor.

THANKS TO ALL.

Thanks for the update with good news. Always helpful.

[SmittydoughF30]

Update - after changing the brake drying code it applied the brakes again in the rain in multiple instances. Cruise control on and off, auto wipers on/off. No apparent pattern.

Since this was a weird ghost it is very possible Two things were happening
1. The brakes were being dried on high instead of low. They fixed that line of code on my first visit.
2. The DSC Unit hydraulic valves were sticking.

The dealer replaced the DSC unit under warranty ($4700 repair for free thanks to Certified Pre Owned warranty) since I brought it in again.
The brake system was keeping the pressure on even after getting my foot off the pedal. This situation got subtly worse over time so I finally brought it back in for service.

I drove it in the rain and the brakes never came on for me, unless I hit the pedal.

[Bgroff28]

SmittydoughF30

Did the replacement of the DSC unit completely fix the self braking issue? I have the exact same problem and the BMW Dealership is telling me it’s the aftermarket pads and rotors.

Thanks

[SmittydoughF30]

Yes, that completely fixed it. Lots of miles since then and never experienced it again. Message me directly and I will send you the service paperwork for DSC replacement.

[miguelsplot]

Originally Posted by SmittydoughF30

Yes, that completely fixed it. Lots of miles since then and never experienced it again. Message me directly and I will send you the service paperwork for DSC replacement.

Hello,

I had the exact same issue, only that yesterday as I was driving home (No rain), my brakes were engaged alot of a sudden and when I came to a stop, they were seized, both front brakes. After I was able to move the car a few feet off the main road, both rotors were red hot and smoking! It may seem that I have a faulty DSC, so I will be looking for a replacement. If you can send me any information I will highly appreciate it. No warranty on my car, so I'll have to do the work myself.

[harmeetsaimbhi]

Hi !

Were you able to resolve this automatic breaking issue after replacing DSC unit ? I'm having the same issue of ABS/DSC unit applying breaks in rain at around 90-100kmph which brings the speed down to 80kmph. And this is happening after short intervals. The worst part is that there are no error logs or codes getting logged into the system. Looking forward to hear back on this thread.

thanks,

[harmeetsaimbhi]

Hi !

Were you able to resolve this automatic breaking issue after replacing DSC unit ? I'm having the same issue of ABS/DSC unit applying breaks in rain at around 90-100kmph which brings the speed down to 80kmph. And this is happening after short intervals. The worst part is that there are no error logs or codes being logged into the system. Looking forward to hear back on this thread.

thanks,

[SmittydoughF30]

Absolutely. DSC was the one and only problem. They replaced under warranty (it was a CPO certified pre owned car) at no cost to me. I have had no brake problems in the years since then. I still have that car.

[nunomaia]

After a long time investigating this problem, I came to a conclusion that it has nothing to do with changing modules, much less spending a fortune for nothing...
The problem is caused by the Dry Braking system, for those who don't know, BMWs have this braking system, which involves "drying" the discs so that they are more effective in rain. This system is activated by the automatic windshield, that is, when it rains and the rain sensor activates and turns on the dry braking system, which starts operating every x time from around 80KM/h. This system should exert 1bar less pressure on the pads in order to only clean water and not be felt on the floor of the vehicle. When this system is malfunctioning, it causes braking (increasingly stronger over time) which causes the car to slow down momentarily. It could also be the problem for some people who feel "pits" lose slight power in some situations. (but the common point is that it is raining)
To resolve the problem there are several options:
1st replace brake oil (who REALLY knows how to do that), the oil could be compromised. Check the braking system.
2º Do not set the windshield to automatic (use manually)
3rd code the car to disable "Dry Braking"

Note: this situation is only for those who do not see any errors on the dashboard, the OBD scan does not show errors in the ABS, DST or DSC system

I hope to help many people because BMW just wants to suck us in...

[SmittydoughF30]

They tried everything to avoid an expensive replacement under warranty - replacing the brake fluid was one initial step (done by BMW).

Disabling features is a great idea if you don't have the time and money to deal with it now but I would not accept turning off features when my car was still under warranty.

Thanks and good luck.

[cbrown]

I have a 2015 328i, F30, rear wheel drive manual transmission I purchased a couple of months ago. I was first having an issue with the brakes not releasing after coming to a full stop. After the test drive I spoke to the sales manager who I had dealt with in the past on my wifes new Mazda's. I explained what was going on during the test drive and he said he would take to the BMW dealer they also owned. A couple of days later I went to pick the car up and the manager said it was hill hold. I owned several VW's with hill hold and none were ever that intrusive. Took the car home and still not satisfied with the explanation. On a rainy day with the rain sensor wipers on the car would brake very hard on its own and I would loose 15 to 20 MPH. Checked the brake fluid and looked like it had never been changed. Removed all the brake fluid from the reservoir and refilled with Napa DOT 4 I had at the house. Brakes were better but still not right. Pulled the wheels off and pressure bled the system. A little better but still not right. Pulled the wheels off again and re lubed the slider pins and cleaned the brake pad mounts, the calipers are single piston. No change. I then called an old Mercedes friend who was also retired and he said to go out and find some loose gravel and hit the brakes hard to get the ABS to kick in. Did that and the brake drag issue subsided temporarily but still came back. He said that one of the valves in the ABS/DSC unit were probably hanging up. Went on E-bay and found the correct ABS/DSC pump for 69 USD. BMW new is 3600 USD I installed the unit, power bled the system and went to a local BMW specialist to recode the unit. Picked up the car and it drove like a completely different car. This morning it was raining hard and drove the car with the rain sensor on, no hard braking. Problem solved. Apparently the old brake fluid corroded the valves in the unit and they would stick. Next thing I am going to do is pressure bleed the entire fleet. Learn something new every day.