I was getting off the freeway and went to break and had to use all my weight on the break pedal to stop the car I was looking online and thought it could either be the brake power booster or the vacuum pump when uncoupled the line near the break fluid and put my finger on it while the car was on I didn’t feel any suction I’m trying to solve this myself because the dealer wants 250$ just for the diagnose and if it’s the booster they want a little over 2k to fix it. Any ideas I can try to figure out the problem and a reliable site to order the parts from the dealer is always more expensive and I would like to avoid that

Definitely sounds like a booster issue. Check your brake fluid as well, I’m not sure on these German cars but I know on American cars I’ve owned in the past, sometimes the brake fluid can corrode the pin inside the booster when it collects too much moisture. If your brake fluid is super old you could give that a shot first, but me personally it sounds like your booster is shot.

okay I’m waiting for Friday when I get paid I was hoping it was the vacuum pump since I didn’t feel any pressure from the hose but the ac works perfect and I think if it was bad the ac wouldn’t work good

You know what's gonna get really expensive is when brakes fail to stop the car... quit driving it until repaired.

Inspect the VACUUM SUPPLY HOSE between pump and booster. Did engine vibration brake plastic fitting?

If hose is fine then suspect one of the check-valves may have failed.
There are two of them: one on each end.

Diagnose the issue first to only replace the bad part with a genuine Mercedes spare.

yeah I’m not driving it don’t want to risk anything I will check those when I get home and give an update

So when you get in the car, press the brake pedal down a few times, then start the car with your foot still on the brake pedal does the pedal go down at all? Or stay stiff?

Have you inspected the vacuum pump, any oil leaking around it, oil in the vacuum line itself?

If it is low/no vacuum im surprised an abs.esp warning doesnt pop on. I see there is a vacuum sensor on the booster.

Have you tried scanning the car for any fault codes?

I never worked on the vacuum system before. Manual shows how to check the vacuum pressure. Is this the location where you checked for pressure?

What has the A/C got to do with anything in the braking system? They are two completely different and independent systems.

I'm sorry but if you think these two systems have anything to do with each other you need to take the car to a workshop and have a qualified mechanic work on the car. Please understand I am being very genuine and in no way derogatory, but you simply don't seem to have the correct knowledge to try and work on these cars yourself.

I came across this thread on vacuum pumps. https://mbworld.org/forums/c-class-w...p-failure.html

okay guys so I was able to get the house off all the way inspected it no damaged I turned the car on and put my finger over the vacuum valve and didn’t feel nothing at all so I’m thinking it’s gotta be that right? I also noticed the big plug part that goes into the break booster sticks on a bit I tried to push it as hard as I could and it wouldn’t budge I think it’s suppose to be like that

to clarify I took the hose off and turned the car on didn’t feel anything and inspected it nothing wrong with it I put it back on I just thought it the vacuum was broke the AC wouldn’t work at all but it does I’m new to working on cars and wanna try to fix it myself before taking it in to the dealer

yeah I he’s saying it’s the booster and I believe that’s that black cylinder under the break fluid? But he says theres no vacuum so I’m wondering what part he’s talking about the break booster or the vacuum pump in the back of the engine in the middle

The booster is the big round thing that looks like an iRobot vacuum cleaner on its side. The cylinder under the brake fluid reservoir is the master cylinder.

There are two main methods of creating a vacuum in the booster: using engine vacuum or a vacuum pump. I believe Mercedes has opted for a vacuum pump to create the necessary vacuum to assist braking.

As Tim mentioned, you should get your car scanned with a Mercedes-specific scanner and not rely on any warning lights.

So, either the vacuum pump is not working correctly or the brake booster has a torn diaphragm and needs to be replaced. You should search YouTube for how to test either component. Mercedes is not unique unless you have an older, S-Class car (e.g., 20+ years) that uses SBC, which you don't.

Sensotronic Brake Control. Let’s leave that dead and buried.

It was amazing in concept, and when it worked.

Implementation and customer education were poor.

I would try to follow the procedure noted above. I got it for the M272 engine but dont see why it would differ for other engines. It says vacuum to the booster should be around 0.75- 0.8 bar under throttle. Thats not alot, around 14psi. Not sure how much you would feel it just using your finger. And thats from the booster port, the other port is smaller and not sure how much pressure that is rated for.

I would be scanning the car first with my scanner for any fault codes. Then I would probably buy an inexpensive pressure gauge and try to see what the vacuum lines show at the booster.

Ahhh, the gauge you have shown appears to read Positive pressure, you need a Vacuum gauge such as this -

Came across an interesting web page showing the vacuum pump operation here: https://www.ms-motorservice.com/int/...nimation)-1145

Looks like both ports should have .7-.9 bar. In the M272 engine one goes to the brake booster and the other goes to control intake and secondary air valves.

okay I will get that tool to try it on Friday and see what’s goin on

And which type of gauge are you intending to buy?

https://a.co/d/aQLqhys I think this is the correct one to be able to test? I am inexperienced in automotive repair but I am motivated to diagnose this problem and fix it with the help of all of you!

That should work.

so I got the tester today and tried it and the needle didn’t move at all I disconnected the house from where it goes through the fire wall to the booster and tried both sides and nothing