Exhaust Flapper Functions & Malfunctions

Owned by Robert Bonamici
Last updated: Mar 18, 2022
3 min read

 

What are “exhaust flappers” / “exhaust valves”?

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” / “exhaust valve” 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.

 

Will a “exhaust flapper” / “exhaust valve” malfunction cause Check Engine Lights (CEL)?

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.

 

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”.

 

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.

 

  • Here is a power plot of a 17 MB C43 AMG with a proper functioning “exhaust flappers” (below)

  • Here is a power plot of a 17 MB C43 AMG with malfunctioning “exhaust flappers” (below)

  • Here is a power plot overlay of a 17 MB C43 AMG with malfunctioning “exhaust flappers” (below) -vs- proper functioning “exhaust flappers” (below)

 

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

 

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

 

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.

 

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