Replacing Brake Vacuum Pressure Sensor

Redd wrote

Adi123 wrote

It's a 15 $ fix! Got the sensor out very easily. Remove the torxscrews on the sensor, unbolt the ABS and make some space. Pull the sensorcable and you got it in your hands!

I checked the numbers on my pressure sensor and found a MAP sensor from a Z4 with the exact same number on eBay for 15$ (besides the production date). Immediately I heard that the pump stoped working overtime. Have been driving it for 3 days now, no codes, no limpmode:party0030:

Any new feedback? Did this Z4 MAP sensor permanently fix the brake vacuum sensor problem?

I would imagine it did. See my thread where I did something similar earlier this year. I used a sensor from a diff pressure sensor on newer cars. All that matters is the numbers match on the sensors. They may have different part numbers but the sensors used are the same

27E4 Brake Vacuum Sensor GOOD NEWS https://www.m3post.com/forums/showthread.php?t=1714625

Nice! $20 sensor vs $200 pressure hose is a huge savings!

Great help. Used a magnet extractor next to the torx because Amazon sent me the wrong torx (non magnetic). All smooth, also used the $20 sensor. Really went very smooth. Used a long reach pliers and bit of a coat hanger but didn’t take anything apart.

Hi All,

I am having similar issues on my car but the code thrown is P1209. Recently changed brake pads and rotors and noticed that the fluid spilled and now I get a loud buzzing noise from the brake pump and limp mode. Will replacing the sensor fix this? Can anyone confirm? Also does someone have the link for the sensor? TIA.

Different application, but same exact sensor and much cheaper.

https://www.fcpeuro.com/products/bmw-manifold-differential-pressure-sensor-13628617097

If fluid spilled on it, it is definitely your issue.

Redd wrote

Any new feedback? Did this Z4 MAP sensor permanently fix the brake vacuum sensor problem?

Yes it did Everything works just like before. For those who are worried about if it will solve their issue, just try it before replacing anything else for 200$

Dpc2u wrote

Different application, but same exact sensor and much cheaper.

https://www.fcpeuro.com/products/bmw-manifold-differential-pressure-sensor-13628617097

If fluid spilled on it, it is definitely your issue.

That was it. I ordered the $20 sensor from Amazon as mentioned in an earlier post and it worked like a charm. Overall took me about an hour start to finish. No more buzzing sound and no more limp mode . Thanks.

Reviving this thread to say that I ordered the whole hose+sensor, getting same code, 27e4. I can't go past 4500 RPM otherwise Limp mode. SES comes on and off randomly.

Will fix sensor, check fuses and report back, this thread helped me out a lot so just in case someone else stumbles upon this, it'll help them too.


Edit: if anyone is having the same issue, the sensor fixed it. My old sensor's gasket was pretty bad, which I assumed was the culprit. Amazing how a tiny gasket can completely cripple my entire engine.

Wish anyone luck who might stumble upon this amazing thread like I did. Removing the sensor was about as hard as putting it on. Two people makes it so much easier. My dad helped me and man I think he had fun lol.

I did this yesterday. I'm wondering what the little gasket on the sensor is made of and if it'd be less expensive just to replace the gasket than buy a new part (I bought a new part on amazon for like $17). Brake Fluid is glycol ethyl, is that right? There appear to be some rubbers that are resistant to glycol ethyl, like EPDM - so what is the sensor's gasket made out of, and would it work if we just swapped out the gasket or O-ring for one made of something else. Anyone have any ideas?

RedCardinal wrote

I did this yesterday. I'm wondering what the little gasket on the sensor is made of and if it'd be less expensive just to replace the gasket than buy a new part (I bought a new part on amazon for like $17). Brake Fluid is glycol ethyl, is that right? There appear to be some rubbers that are resistant to glycol ethyl, like EPDM - so what is the sensor's gasket made out of, and would it work if we just swapped out the gasket or O-ring for one made of something else. Anyone have any ideas?

In most cases it is not the o-ring that is the issue. If even a couple of drops of brake fluid weep onto the wiring connection it shorts the sensor out. For whatever reason it is extremely sensitive. Glad you got it swapped and I assume it cured your problem.

Dpc2u wrote

In most cases it is not the o-ring that is the issue. If even a couple of drops of brake fluid weep onto the wiring connection it shorts the sensor out. For whatever reason it is extremely sensitive. Glad you got it swapped and I assume it cured your problem.

Thank you! Your remark about it being a job that requires some finesse kept popping into my head. I felt like I was playing "Operator" (the Milton Bradley game) while trying to remove screws with magnet telescoping thingy - sometimes the magnet wants to stick to something else and twice I dropped a screw down down down into the hole (I was able to retrieve them).

My damaged part looked just like someone else's in this thread - the o-ring was beat up and fraying.

But, on thinking on it now there, there was a good amount of vacuum suction noise as I removed the part, so I suppose that you're right and the o-ring wasn't the problem. huh.

The part I bought was cheap and made in china so I hope it lasts, I don't want to do this replacement again lmao.

I found that a wire hanger was pretty useful, as was the large flathead screwdriver to move the part so that I could better access the screws to unscrew and re-screw it down: Actually the flathead was essential, being able to move this thing a bit is really helpful. I also unbolted the ABS and lifted it over its mounting screws which gave me a bit more room, as did un-snapping the firewall on the other side where the vacuum tube passes through it, that gave me some more angles to work with. Definitely needed a flashlight even though I was working in broad daylight.

Later I was trying to picture what kind of hypothetical tool we could create that would make this job much easier, like some kind of metal angled tounge-depresser with a hole in it to match the nub on top of the sensor, that you could slip under the master cylinder and hook the sensor and then pull it over the tube and press it down. But I suppose the screwdriver and hanger and just time is enough.

I'll add that I did wonder why a part that's so sensitive to brake fluid is so difficult to get to and is located right under the master cylinder which is, of course, all filled with brake fluid;

What are the chances of the sensor going bad after the brake fluid overflow? I found a small puddle near the front jack stand and traced it back to the reservoir after changing all 4 pads. I looked at the sensor and it doesn't look wet including where it plugs into the wires. Where does it get shorted?

Great thread, thank you! Recently picked up an e90 and have been hearing an intermittent humming/vibrating under dash/in front fender....searching led me here and believe it is a bad sensor, no codes yet. I ended up ordering the hose from my local dealer that has the sensor on it.

Is it easier to just replace the entire hose or just the sensor? I'll tackle it over the next few days....

2011e91 wrote

Great thread, thank you! Recently picked up an e90 and have been hearing an intermittent humming/vibrating under dash/in front fender....searching led me here and believe it is a bad sensor, no codes yet. I ended up ordering the hose from my local dealer that has the sensor on it.

Is it easier to just replace the entire hose or just the sensor? I'll tackle it over the next few days....

You only need to do the sensor.

I'd take back the part you bought and just buy part # 13628657300. Its labeled as a diff pressure sensor but its the same sensor on the overly priced entire hose assembly. I think oem is like $85 and oe is $50.

k_mann wrote

2011e91 wrote

Great thread, thank you! Recently picked up an e90 and have been hearing an intermittent humming/vibrating under dash/in front fender....searching led me here and believe it is a bad sensor, no codes yet. I ended up ordering the hose from my local dealer that has the sensor on it.

Is it easier to just replace the entire hose or just the sensor? I'll tackle it over the next few days....

You only need to do the sensor.

I'd take back the part you bought and just buy part # 13628657300. Its labeled as a diff pressure sensor but its the same sensor on the overly priced entire hose assembly. I think oem is like $85 and oe is $50.

thank you, unfortunately already committed to the complete unit but before I tear into it I was wondering if it's easier to deal with the few plugs of replacing the hose or if it's easier to just replace the sensor? I've looked but couldn't find a DIY of replacing the hose itself.

I say to myself how difficult can 3 plugs be; famous last words??

2011e91 wrote

k_mann wrote

2011e91 wrote

Great thread, thank you! Recently picked up an e90 and have been hearing an intermittent humming/vibrating under dash/in front fender....searching led me here and believe it is a bad sensor, no codes yet. I ended up ordering the hose from my local dealer that has the sensor on it.

Is it easier to just replace the entire hose or just the sensor? I'll tackle it over the next few days....

You only need to do the sensor.

I'd take back the part you bought and just buy part # 13628657300. Its labeled as a diff pressure sensor but its the same sensor on the overly priced entire hose assembly. I think oem is like $85 and oe is $50.

thank you, unfortunately already committed to the complete unit but before I tear into it I was wondering if it's easier to deal with the few plugs of replacing the hose or if it's easier to just replace the sensor? I've looked but couldn't find a DIY of replacing the hose itself.

I say to myself how difficult can 3 plugs be; famous last words??

I have done a few for others, but only once with the hose assembly. Definitely easier to replace just the sensor In my experience. As long as you have the right surgical tools, it can be done in 30 minutes or less!

Dpc2u wrote

2011e91 wrote

k_mann wrote

2011e91 wrote

Great thread, thank you! Recently picked up an e90 and have been hearing an intermittent humming/vibrating under dash/in front fender....searching led me here and believe it is a bad sensor, no codes yet. I ended up ordering the hose from my local dealer that has the sensor on it.

Is it easier to just replace the entire hose or just the sensor? I'll tackle it over the next few days....

You only need to do the sensor.

I'd take back the part you bought and just buy part # 13628657300. Its labeled as a diff pressure sensor but its the same sensor on the overly priced entire hose assembly. I think oem is like $85 and oe is $50.

thank you, unfortunately already committed to the complete unit but before I tear into it I was wondering if it's easier to deal with the few plugs of replacing the hose or if it's easier to just replace the sensor? I've looked but couldn't find a DIY of replacing the hose itself.

I say to myself how difficult can 3 plugs be; famous last words??

I have done a few for others, but only once with the hose assembly. Definitely easier to replace just the sensor In my experience. As long as you have the right surgical tools, it can be done in 30 minutes or less!

Thank you, replacing the sensor it is!

Mission accomplished! The car is new to me so still learning details but took about an hour replacing just the sensor without removing anything but the cabin filter cover and the tray underneath. Did not touch the abs block, master cylinder or plastic divider. Stuffed a bright colored rag underneath the sensor/hoses to catch anything and also helped viewing. Someone else mentioned it was like playing Operation, very true.

The dealer I purchased the car from last month replaced the front brake rotors and pads; sure enough the sensor was wet from brake fluid which apparently caused the failure and subsequent intermittent running of the pump. I wasn't getting any error codes.

There was residue vacuum in the hose (could hear it as I removed existing sensor) so the failure seems to be the senor itself, not the gasket.

Thank you!

2011e91 wrote

Mission accomplished!

Well done! 🧰🔧

Adding my piece to this thread, you'll also find other tips here: https://www.m3post.com/forums/showthread.php?t=1714625


I had same issues others have described. limp mode with 27E4 engine code - and intermittent buzzing from the vacuum pump heard in the cabin, sounding like its coming from behind the dash.

BPMSport helped me out and directed me to this brake boost pressure sensor being the culprit and I ordered the sensor only from a regional BMW dealer. They are available generic on Amazon for as cheap as $20 but delivery on those were out 1-4 weeks airmail from China.

My contributions:
I have a deep adolescent and biologic drive to unfasten things. Just imagine what is behind this once I get it unfastened. I get breathless, my mind fogs, I can't do anything until I get it unfastened to see what is beneath. If you are like me in this way, RESIST. As a couple others above have mentioned - I did not need to remove the reservoir, did not need to disconnect the ABS pump, did not need to disconnect the vacuum line to remove the shroud.

I used a rigid hooked grill tool to nudge the vacuum line the sensor sits in. this allowed me to disconnect the two #15 torx screws which I retrieved with a magnet. GENTLY pulling on the wiring harness and using said hooked tool - I dislodged the sensor and pulled it out from beneath the reservoir. When I dislodged the sensor - I did hear a release of vacuum.

While the brake fluid had not been flushed/changed in 2 years (it's now on the list), I had disconnected the brake fluid reservoir cap during my Harrop install to route my boost sensor hose - and I think I got a few drops of brake fluid splashed onto the sensor when I did that - causing the short. There's evidence of fouling on the surface of the old sensor seen in the photo - but also the o ring is a little shredded.

I installed the new sensor into the wiring harness and carefully routed it back down in place. Once I had the holes lined up - I used a skinny and malleable magnet tool to feed the torx screws into the hole and got it started 1/4 - 1/2 of a turn into the threads. that was enough to remove the magnet then get a proper torx bit on a couple of 1/8" extensions into place and screw the sensor down. I used the grill tool to nudge the vacuum hose the sensor sits in during this phase as well - mostly to get the screw holes in position so they can be reached from above without removing the reservoir.

After the job was done, I routed a 2" x 3" piece of neoprene rubber atop the sensor area to attempt to prevent this in the future. at the moment it's not secured down but is caged by the wiring and ABS brake lines so I think it will just ride atop the sensor without issue.

M'EM wrote

That was it. I ordered the $20 sensor from Amazon as mentioned in an earlier post and it worked like a charm. Overall took me about an hour start to finish. No more buzzing sound and no more limp mode . Thanks.

Seconding this! Got my Amazon sensor for 17 bucks in 2 days. Looked identical to what I took out and has so far solved the buzzing and limp mode issues. Thankful for this thread!

Anyone else planning on leaving a shop rag over the sensor to avoid the issue in the future? Doesn't look like a part of the engine that gets particularly warm.