Brake Vacuum Pump Noise?

Hey all,

An electronic sound coming from the engine bay surfaced while I was driving this week. At first I thought it was coming from under the dash in the cabin, but then I noticed it came on when I was on my brake pedal. Some context, I did get some work done on my E90 last week and I got fluid and pads changed out.

The fluid is Motul RBF 600. 2 bottles were used for the job. One for the flush, the second for the fill.

I've been doing some digging on the forum and so far I'm thinking it's related to the brake vacuum pump? I would like to know if I'm diagnosing this right.

Here is a video:

*Update*: Changed the sensor out and the issue is resolved.

Did brake fluid spill out of the reservoir? Someone else has the same issue as you where it went off every time he pressed the brake pedal. There's a sensor under the res that can short out

I'll need to ask the shop. I didn't do the work myself. Am I in a pinch? I have a track day coming up on Monday, and I'm hoping I can still go. If I can, I'd get the sensor replaced soon after.

It's not normal for the pump to work after braking? Mine goes off after parking, pulling out of a spot, hard braking, etc and I think that's pretty normal.

Ximian wrote

It's not normal for the pump to work after braking? Mine goes off after parking, pulling out of a spot, hard braking, etc and I think that's pretty normal.

If its going off every time you hit the pedal.

ItsGary wrote

Ximian wrote

It's not normal for the pump to work after braking? Mine goes off after parking, pulling out of a spot, hard braking, etc and I think that's pretty normal.

If its going off every time you hit the pedal.

It goes off after about 4 or 5 pumps.

tougetrained wrote

It goes off after about 4 or 5 pumps.

Mine is about 3 to 4 with Motul RBF660 or if the pedal goes all the way down. 1 to 3 pumps with OEM fluid. It's always done it as far as I know and nobody that's worked on the car has mentioned it before. I don't think it's a significant problem.

My brake vacuum pump became more active just before my brake vacuum pressure sensor failed. I'd be prepared for that eventuality.

If any fluid got on the sensor, it will get progressively worse and eventually you will go into limp with the following code - 27E3: Vacuum sensor, brake booster, plausibility. If they collapsed the calipers without removing some fluid from the master cylinder or cracking the bleeder, it will push fluid back to the master cylinder and some spills over and drips on the sensor.

ItsGary wrote

Did brake fluid spill out of the reservoir? Someone else has the same issue as you where it went off every time he pressed the brake pedal. There's a sensor under the res that can short out

This is exactly what happened to me. While installing my BBK got some brake fluid on the brake vacuum sensor and shorted it out. Shortly after the pump would stay on and my car would go into limp mode under heavy throttle. It was a pain to replace the sensor since its in such a small compartment, but definitely a diy-able job. Hopefully the OP has small hands

I had the same thing happen as others are saying.

I did a full flush and refill and must of spilled a tiny bit of fluid. Unfortunately their is a vacuum sensor just below the brake fluid reservoir. The fluid runs down and gets inside the sensor and destroys it.

Starts off making that noise and will eventually trigger a CEL and send you into limp mode. You will need to replace the sensor. Its a very tight area but do able without removing the reservoir.


Here is the part you will need and BMW will not sell just the sensor, you have to buy the hose as well. I kept my old hose installed. I just swapped the sensor and cleaned everything very well to make sure no old fluid was on the hose.
https://www.getbmwparts.com/oem-parts/bmw-vacuum-hose-34302283605?c=Zz1ib2R5JnM9bWFzdGVyLWN5bGluZGVyLWNvbXBvbmVudHMtb24tZGFzaC1wYW5lbCZsPTMmbj1Bc3NlbWJsaWVzIFBhZ2UmYT1ibXcmbz1tMyZ5PTIwMTImdD1iYXNlJmU9NC0wbC12OC1nYXM%3D

Dpc2u wrote

If any fluid got on the sensor, it will get progressively worse and eventually you will go into limp with the following code - 27E3: Vacuum sensor, brake booster, plausibility. If they collapsed the calipers without removing some fluid from the master cylinder or cracking the bleeder, it will push fluid back to the master cylinder and some spills over and drips on the sensor.

+1

I had crippling limp mode all day at the track yesterday with code 27E4 (only got a few warmup laps in the first session, then cleared codes but couldn't get an entire lap in for the next few sessions before giving up for the day). I checked the forum, remembered overflowing a bit of brake fluid a month of two ago when pressing caliper pistons back, and then checked the sensor to find it covered in brake fluid. The sensor lasted a couple months and almost 5 track days before dying, but it really sucked when it happened at the track.

If you track regularly I'd recommend ordering from FCPeuro in case you accidentally do it again, since brake fluid and pad changes become much more common.

Ximian wrote

Mine is about 3 to 4 with Motul RBF660 or if the pedal goes all the way down. 1 to 3 pumps with OEM fluid. It's always done it as far as I know and nobody that's worked on the car has mentioned it before. I don't think it's a significant problem.

It's worth mentioning that it only occurs on track for me. Maybe my street driving doesn't use enough braking? Dunno Definitely worth checking your sensor for wetness though, especially if you have any upcoming track days.

Hey all,

As mentioned by those in this thread, it was indeed the sensor. I took it back to my shop and they replaced just in time. Everything was back to normal and I made it to my track day. First time out with my E90 and it was great.

So how often does the pump come on when everything is working fine?

Mine is pretty frequent and since it's been doing it for over two years without a limp mode, it's probably not the sensor. It only runs for like 5-6 seconds at a time.

Ximian wrote

So how often does the pump come on when everything is working fine?

Mine is pretty frequent and since it's been doing it for over two years without a limp mode, it's probably not the sensor. It only runs for like 5-6 seconds at a time.

With the bad sensor I would not get errors or limp at all during street driving. It only happened on track. So, if you aren't tracking it may still be possible that your sensor is bad. Edit: Just realized I already said that a couple posts up. Only 31 and I'm already repeating stories :-(. And I'm pretty sure you're tracking regularly so N/A. Sorry.

I don't remember ever hearing the pump turn on before the sensor got fried. With the fried sensor, it turned on with every hard brake pedal depression. After I replaced the sensor, I haven't heard it turn on at all.

So I had this crippling problem yesterday. Had to restart my car every other mile just to get home. Pulled the code and it was 27e2. I figured it was the sensor since I spilled a little fluid topping off when flushing the other day.

I took apart the micro filter cover and expansion tank cover, took some Damp shop towel with IPA, cleaned up all the vacuum lines and electrical connectors. Then I saw that I overfilled the brake fluid slightly above max line. So I suctioned out some brake fluid until it was between min and max. Proceeded to drive the car hard for about 100 miles with no limp mode. I'm hoping my limp mode was due to brake fluid overfill and not sensor.

Moral of the story: check your brake fluid level before replacing sensor.

Went to the dealer today to get the blower motor wiring recall done so tried to get a second opinion. Couldn't get the vacuum pump going at all today doing the same things that set it off the last few years. Either the cooler temperature today (gasket around the sensor deteriorating?) has something to do with it or it's fixed itself because that's a thing that happens.

Either way, I'll be following the DIY in https://www.m3post.com/forums/showthread.php?t=1338052 soon. Dealer quoted over $1300 to replace the sensor/hose, most of it going toward labor, so I'll be using that number to justify other purchases to the spouse.

$1300? Wow. Cost me $100 and about an hour in the garage.

Dpc2u wrote

$1300? Wow. Cost me $100 and about an hour in the garage.

+1 I have big hands and swapping the sensor took 30min without removing or even unbolting any components around the sensor (I just unclipped and slightly moved the small plastic partition wall section that the vacuum hose passes through into the engine bay). I used long needle-nosed plier to remove and replace sensor and a telescoping magnet to remove and replace the torx screws.

tougetrained wrote

Hey all,

An electronic sound coming from the engine bay surfaced while I was driving this week. At first I thought it was coming from under the dash in the cabin, but then I noticed it came on when I was on my brake pedal. Some context, I did get some work done on my E90 last week and I got fluid and pads changed out.

The fluid is Motul RBF 600. 2 bottles were used for the job. One for the flush, the second for the fill.

I've been doing some digging on the forum and so far I'm thinking it's related to the brake vacuum pump? I would like to know if I'm diagnosing this right.

Here is a video:

*Update*: Changed the sensor out and the issue is resolved.

Hi

Mine a e93 m3

Whenever i entered my car with ignition on before engine crank, i hear a loud buzzing sound from the pax door (rhd), cant seem to hear it after i crank

Should i just change the pump

Probably your brake vacuum sensor malfunction happen soon, just be prepared. My car have the same problem and eventually sensor died and car goes in to limp mode.

Resolved this a while ago^. Just replaced the part. I did go into limp mode at the time.