MBWorld Members,


We would like to address this topic as most people do not know the function of the "exhaust flappers", what they actually do and what happens when they are not functioning properly.



What are "exhaust flappers"?

Certain MB vehicle's come equipped with Mercedes-Benz exhaust flap technology (PE models) which adjusts air flow through the exhaust. This adjustment affects sound as well as performance.



How does the "exhaust flapper" work?

The MB exhaust flapper technology is adjustable through the "dynamic select" modes (eco, comfort, sport, sport +). When changing through the modes, the "exhaust flappers" located on the inside of the muffler closest to the bumper, allow the "exhaust flappers" to change angle which in turn allow more or less air to pass through. This change will affect the vehicles performance and sound.



Check Engine Lights?

This specific error will cause a check engine light (CEL) also referred to as a diagnostic trouble code (DTC) or malfunction indication light (MIL). However, since the exhaust flapper is not an engine issue, the code will come up as a "soft code" and not trigger the dash light.



What is a "soft code"?

A "soft code" is a code that is present in the ECU however not displayed on the dash. The code will be seen through an on-board diagnostic scanner (OBD) but not trigger a physical light on the dash. The dash will only indicate a "hard code".



What is a "hard code"?

A "hard code" is displayed on the dash, as referred to above as CEL, DTC, and or MIL, showing the operator and/or driver of the vehicle that their is a mechanical issue.


Power Plots:

Here is a power plot of a 17 MB C43 AMG with a proper functioning "exhaust flappers"





So what would happen if your vehicle had a "exhaust flapper" malfunction?





Power Plot Overlay (functioning -vs- malfunctioning):





What can you do to fix this issue?

Most of members vehicle's are still under warranty so we would advise going to your dealer to have this fix as it could be the following:

- Exhaust Flapper is jammed
- Damaged Exhaust Flapper
- Damaged Exhaust Flapper Arm
- Bad Exhaust Flapper Module



Will a "ecu tune" fix this issue?

Any ECU upgrade, piggy back and/or ECU tune, will not fix this issue. We advise to fix the issue before getting any tune.



What if I am already been "tuned" or installed a "piggy back"?

If you have already started upgrading your vehicle and this issue has happened, you will need to address it as you are not running at full potential and can possibly cause further damage especially those running piggy-back style systems were the ECU signals are being simulated, manipulated and/or changed.



Does this issue affect boost?

Yes it does. Boost levels are drastically dropped due to the malfunction. On a "ECU tuned" vehicle, it can cause improper boost stability.





We hope this was informative as we continue our support for the community.

 

 

The vehicle is showing this loss of power at wheels when the flapper is malfunctioning / not working.

When the flapper is malfunctioning, the loss of power is due to the airflow being blocked in the exhaust system due to the flapper malfunction.

 

 

With that kind of loss it would OBVIOUSLY BE FELT.

 

Have you ever worked for mercedes or been a tuner?

 

 

LS motors are a little different from these beautiful german engines.

 

I have tuned a lot of cars on Forza and i can tell you that exhaust flow can really hurt the car.

 

HMMMM now this is interesting for the people who have a Active Sound Module I wonder if this is happening

I have one and have always felt a difference when I have the valves open apposed to having them in the "stock" setting on smooth lower RPM throttle imput



I

 

Here is my theroy.

It is a soft CEL, also meaning a soft limp mode. The car would cap its hp and torque at both 250.
Go into dynamic select mode and engine data would confirm.

Also when the valves fail, no damage is being done. So no matter what you do your ECU would simply cut power for safety.

 

 

Great info here. Something is not clear to me, are the exhaust flaps the same thing as the exhaust valves?

 

Hey I have a c63s with potentially the same issue.. what obd reader will see this is the issue? My shop says it probably is but I want to confirm before dropping another 3-4k, I just can’t find a scanner that works

 

Yes, I would recommend this before spending the money to guarantee this is the issue.

Correct, standard scanners as well as off the shelf generic can not read specific modules or detect vehicle specific module error codes.

Our @AMR Performance COMPORT Pro Tuning Suite has advanced scanning methods designed for MB, no different than factory tooling. You can also scan with MB Xentry tools.

 

Exhaust valves are in the engine and allow exhaust gasses out of the cylinders.
Exhaust flaps are in the muffler and control the flow of exhaust through that system.

 

Is the PE the same exhaust system as a non PE just has the flapper valve? Or is the complete exhaust different? Does the PE add HP, or is it just for extra sound only?

 

I was told sound only, which is why I'm fine with not having it.

 

First generation flapper:

 

Would you suggest removing the flappers? I want it loud, which the flapper module I have installed allows me to do that.

i have a loss of 100whp!

thank you!

 

You can not just remove the flappers as the ECU as well as additional modules would see them as damaged causing the same outcome to occur.

The correct method would be to repair the flappers.

 

does this same power loss issue apply to those that have the renntech/ ASR module that overrides the OEM programming and keeps the flaps 100% open , 100%of the time ?

 

Doesn’t matter. That only holds the back 2 flaps open, it’s the center one on the mid pipe that’s the problem. Get a new exhaust

 

Ummmm i dont have to get a new anything(but you on the other hand should get new info). Especially since the c43 only has 2 flaps in the back.

No flaps on the mid-pipe

 

Yea maybe the 43 is different the 63 shares the same issue and that’s the cause