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Brake servo vacuum sensor error ?

88K views 31 replies 16 participants last post by  alamayub29 
#1 ·
Hi all,

I have a 2010 120d coupe / 38k miles / well looked after ....with stop / start warning light coming on on the dash..an ( A! ).

I took the car to an indie BMW a garage in Stoke on Trent and initially it was not showing any fault codes at all.....they then established that there was no signal from the neutral position sensor ...so that has been replaced ...warning light remained on ....they then did a full recode...and fully charged the battery..warning light is still on ! It is now showing a fault as " brake servo vacuum sensor error" ?

This has them stumped ?

Has anybody else had a similar issue or can recommend a fix ...?

Currently pocket is £250 lighter and I have the distinct feeling that it's the blind leading the blind ?

Any help welcome ! Currently warning light chimes on start up and shut down .
 
#3 ·
marco_polo said:
Sounds like a basic vacuum leak to me, the Stop/Start won't function if that sensor says there isn't enough vacuum in the servo. Or it will restart the engine automatically if the vacuum drops.

I believe the trigger pressure is 0.5 Bar.
Hi,

Thanks for the reply. It could be that simple !! I will get it looked at after Xmas ...

The aforementioned sensor doesn't appear on an exploded view of brake servo...which adds to the confusion ? I don't know if it's incorporated somewhere else ? As the car and brakes currently work fine the assumption was a faulty sensor ?

I am just trying to avoid having a scenario where everything possible is replaced and the problem still exists.

Thanks again.
 
#6 ·
#7 ·
Hi there, just picked up this thread......I have the same A! Start/stop error. I have the OBD bmwhat app (really good btw) which brings back the same fault code 004AFB 'brake vacuum sensor'. DI'd you manage to get to the bottom of this?.....as kind of feel that you know more than bmw :?

Regards
 
#11 ·
Hi- my start stop hasn't worked for a while (shows fault light) and got my local indi to test it while in for service.
I too have a vacuum sensor failure :-(
They want about £200 to do the job including re-coding, the part being £100 +VAT.
I've had a look and it looks like a real pain to get to the sensor without stripping stuff out.

Was thinking it might prise out with a long set of pliers with the replacement going back the same way.
Has anyone tried this? Is it as simple as pulling it out and pushing the new one in or is there something holding the sensor in place?
 
#17 ·
Did mine a few days ago-
It was reasonably easy- just needed to remove the polen filter housing and the plastic tray that it sits on to access- I think it was six or eight bolts in total.

It was still a fiddle to get the sensor out- nice to hear the vacuum hiss when it came out. I used a couple of long screw drivers to prise it out. and the same to locate and push the new sensor back in. The rubber grommet looked prety clean, so didn't bother removing it.

No longer have the warning light and anoying sound on start up, which is a result, but the stop start isn't working- I wonder whether there is a fault code that needs re-setting?

The part number is different from my original one. As far as I can tell there is a new version- my original part number is 6786746 (now obsolete). The replacement is 6875605
 
#18 ·
jager66 said:
Did mine a few days ago-
It was reasonably easy- just needed to remove the polen filter housing and the plastic tray that it sits on to access- I think it was six or eight bolts in total.

It was still a fiddle to get the sensor out- nice to hear the vacuum hiss when it came out. I used a couple of long screw drivers to prise it out. and the same to locate and push the new sensor back in. The rubber grommet looked prety clean, so didn't bother removing it.

No longer have the warning light and anoying sound on start up, which is a result, but the stop start isn't working- I wonder whether there is a fault code that needs re-setting?

The part number is different from my original one. As far as I can tell there is a new version- my original part number is 6786746 (now obsolete). The replacement is 6875605
Hi ya,did you get it sorted? I got the same problem so will probably come up against that too.
I really love my BM but it's one thing after another lol.
 
#20 ·
The_Coach said:
Just for the record....the brake servo pressure sensor was actually faulty. ....Replaced and now functioning fine.

Finally found a good independent in Dublin, who knows his stuff.
Was it paul by any chance ???

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#21 ·
Replaced break preasure sensor in my f10 which affected stop/ start.
Its not so dificult to do it, first of all you need to remove electric box, aluminium bar to get access. There was no need even to remove a tank. I was strugling to put it back other than that was not too bad.
 

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#22 ·
Does anyone have experience with the "4AFB Brake Vacuum pressure sensor, signal" error persisting even after a replacement part? The part was not OEM (£20 off eBay). I have a 2011 116d. I will try another part and give an update.

EDIT:

I tried another more expensive sensor but the error remained. Looked for electrical faults between the sensor connector and ECU. Everything looked normal with the sensor getting 5V. Finally decided to just buy an OEM BMW one and SUCCESS. I would be very sceptical about these cheaper sensors as both didn't work...
 
#24 ·
Does anyone have any experience with Frunimall brand sensors from Amazon? Sub-£20 and the reviews are either brilliant or terrible.
One example is but most of the other ones listed about the same price seem to claim to be the same brand. I'll also take suggestions if anyone else has had success with a low-priced part.
The next most affordable option I have found with not much looking is a Vemo branded part from AutoDoc for £70.54
 
#25 ·
Just to update I bought the following:
I'm pretty sure it is the same as I linked earlier, but less money, and 2 day delivery on prime when ordered late evening.

It's a pig to fit but worked once I got it in and cleared the codes. Just hope it stays working for a decent length of time. This also fixed the auto-stop-start error I was getting, so no annoying bong any more..... Except when it's cold and I get the ice warning.
 
#26 ·
Just to update I bought the following: I'm pretty sure it is the same as I linked earlier, but less money, and 2 day delivery on prime when ordered late evening. It's a pig to fit but worked once I got it in and cleared the codes. Just hope it stays working for a decent length of time. This also fixed the auto-stop-start error I was getting, so no annoying bong any more..... Except when it's cold and I get the ice warning.
Just purchased this part myself - a big thank you as it's saved me £100 over the BMW part! Will fit it tomorrow and cross my fingers that Carly can clear the error.....
 
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