2014 35d Brake System Warnings/Low Vacuum

[Jaywlambert]

Hey guys,

A day after changing my oil, I started getting these "drive moderately" warnings. First time it came on it was in the middle of a two hour drive, I turned the car off then on again and it went away until the very last minute of the drive. When the warning is off, it stops normally. Once the warning kicks on, the pedal is a bit funky like the booster isn't working 100%. The warning would go away for a while at first, and come back on mostly while turning. Now it comes on as soon as I start it up basically.

2014 x5 35d, 101k miles. Brake fluid is full, no noticeable leaks/cracks around the booster or the vac line that runs from it (which was my first thought since it goes near the oil dipstick that I had just touched). I checked the pedal a few hours after last starting it, and it seems like there was still a ton of vacuum at the booster which makes me want to rule out an actual leak.

Any insights/things to check? No idea how complicated the braking system is on these, can the code being thrown change the way the booster functions? It only feels weird if the code is on which makes me think this is a bad sensor or something.

[Clifton]

I'd revisit the vacuum line to the booster. All it takes is a hairline crack and you have a vac leak. It's the only plausible explanation since your brakes were fine before the oil change. I'd start there (vac line) since the brake boosters aren't common to fail.

There are probably some YouTube videos with clever ways to test if you don't have access to smoke machine.

[Jaywlambert]

Originally Posted by Clifton

I'd revisit the vacuum line to the booster. All it takes is a hairline crack and you have a vac leak. It's the only plausible explanation since your brakes were fine before the oil change. I'd start there (vac line) since the brake boosters aren't common to fail.

There are probably some YouTube videos with clever ways to test if you don't have access to smoke machine.

What's confusing to me is that it's intermittent. I took the car out for a short drive today, no issues. I sat there and pumped the brakes for a while, drove for a bit, came back and pumped the brakes again...no warning.


I'll admit I don't know enough about how these systems work, does the ecu have control over the vacuum pump or is it purely mechanical? The way the pedal feels changes instantaneously when the warning comes up...I'm just unsure if the warning is the symptom or the cause of that.


Either way, I'll definitely take a better look at that hose when it's nice out. It would have to be super brittle to crack from my hand bumping it while I checked the oil but stranger things have happened.

[Jaywlambert]

On a related note, wtf is that second code all about? At first I assumed it was just because of the vacuum fault, but now I'm not sure lol

[Jaywlambert]

Originally Posted by Jaywlambert

On a related note, wtf is that second code all about? At first I assumed it was just because of the vacuum fault, but now I'm not sure lol

Smoke test found a solenoid that was leaking...but when I bypassed those lines I still had the same low vac issue so I'm wondering if the pressure from the smoke machine did it in. Bypassed basically everything other than the main vac line, checked the one-way valve on the booster line, still the same issue.

My last thought was to look at the crankcase breather diaphragm but I basically had to break the cover off to look at it. No tears but it was a bit worn where it seals.

Is anyone real familiar with the breather/vacuum setup on the N57? Seems like there is basically no info out there other than some stuff from europe in languages I don't understand lol

[Jaywlambert]

...ended up being a faulty vacuum/pressure sensor on the booster. It threw me off since it was still sending a reading/moving as I drove. Tested with a vacuum tester (which should have been my first move) and realized the sensor was just way off.

[Clifton]

Jaywlambert - Thanks for keeping the thread updated. Is there any other detail on how you narrowed it down or what it took replace? Simple Plug and play? Part Number?

Biggy Thanks!