Hissing noise from brake pedal when released - Mercedes GLC 300 AMG premium plus (2020 Model)

Waj · Mar 18, 2022

Hi all ,

I have a encountered a problem recently with my GLC 300 which was purchased new in 2020.
A problem developed that when releasing the brake pedal, a hissing noise comes from the brake pedal - similar to a vacuum leak sort of. The noise is very annoying.
I have taken the car to a Mercedes service centre back in November last year; they checked and said nothing is wrong with the car. I was bit annoyed as clearly something is not right either. This service centre is not my usual dealer; I had to go there, as no appointments were available at my usual Mercedes dealer.
Has anyone experienced this? Car is still under warranty; I am planning to take to mu usual dealer next week along with the service.
Searching the web, I can see few posts regarding this.

Any details on this is much appreciated!

Jmerc · Mar 27, 2022

Hi, I've just collected a 2021 GLC300e hybrid, and I've noticed a noise sometimes when I transfer my foot to the accelerator pedal? Didn't have it on my last GLC. Is yours definitely coming from the brake pedal? Jamie

Waj · May 10, 2022

DZM · Apr 19, 2022

Have the same issue GLC 300 2018. It happens after about 15 mins of driving and only when warm/above 70 F outside.
Went to dealer twice, they didn't find anything wrong.

Waj · May 10, 2022

Keefrto · Apr 25, 2022

Happens to me twice a year. During cold temps here in Alberta, i noticed this and was like wtf the first year but it quickly became clear that it didnt happen in warmer weather. Just my experience in winter.

Waj · May 10, 2022

Waj · May 10, 2022

Yes spot on... it comes after 15 mins of driving and hissing sound gets intensified more you drive from there...

i have come across that some say it’s air leak from break booster...
I took the car once to the dealer and they checked and say nothing wrong...but I believe something not correct

Waj · May 10, 2022

my car is still under warranty and if something is wrong with the break booster, a probably a costly repair..... i want to get it done now before the warranty expires.
but I am not happy with the tratemnet of the Merc dealers, i have taken my car today for annual service, and want them to have a look again on this issue.

Waj · May 10, 2022

Yes it comes definitely from the brake pedal and when the pedal is released...... generally noise comes after 15 mins of driving and hissing sound gets intensified more you drive from there...

There are few posts on the web...regarding this...
I also recently felt a sudden loss of power when accelerating from stand still, looking at some blogs on the web both these problems are interconnected.

i have come across that some say it’s air leak from break booster...
I took the car once to the dealer today…. Will see what they say.

achiste · Jul 7, 2022

I have this sound also. Mine is a 2020 GLC 300 and the hissing is not consistent. It seems random. Then when I press the brake pedal, I just discovered it will stop. What is this??

Waj · Aug 15, 2022

Hi there,
This is definitely early signs of failing break booster. Mine was finally changed last month under warranty. I have the same model as you GLC 300 purchased in March 2020.
Car had done only 4500 miles when the problem started late last year. Shocking poor quality and seems like a wider issue as lot of people are experiencing this.
Also I managed to speak to MB senior technician and he said he replaced few of these.

Jmerc said:
Hi, I've just collected a 2021 GLC300e hybrid, and I've noticed a noise sometimes when I transfer my foot to the accelerator pedal? Didn't have it on my last GLC. Is yours definitely coming from the brake pedal? Jamie
Get it replaced under warranty quickly....other wise it will be costly!

Cheers

Gecko · Aug 3, 2023

Is the problem got fixed after they replaced the break booster? my glc250 has same issue but it is out of warranty

Waj said:
Hi there, This is definitely early signs of failing break booster. Mine was finally changed last month under warranty. I have the same model as you GLC 300 purchased in March 2020. Car had done only 4500 miles when the problem started late last year. Shocking poor quality and seems like a wider issue as lot of people are experiencing this. Also I managed to speak to MB senior technician and he said he replaced few of these.

xkristenmatteix · Dec 28, 2024

Hi I am also experiencing the same hissing noise on my 2020 glc 300 and the mechanics at the merc dealer are saying nothing is wrong. The sound is extremely annoying. Has anyone found that replacing the break booster fixed the problem? Really appreciate any advice

JJP · Mar 25, 2025

Hi guys my 2020 GLC coupe is also making the same noise - hissing/ air kind of sound when depressing the brakes. I’ve taken it to 2 garages and they can’t find any faults although I know that this sound is not normal! Did anyone find a solution?

mrrosado · Apr 26, 2025

I just had my booster replaced under warranty for the exact same issue. I had to make a video to finally get them to take action. They initially tried telling me it was normal and even brought out another customer’s car to show me the same noise. Regardless, a luxury vehicle should not be making those kinds of sounds. Now, with the new booster installed, I don’t hear a thing.

Hissing noise from brake pedal when released - Mercedes GLC 300 AMG premium plus (2020 Model)

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