M3/M4 Exhaust Flap — Always Open
The S55's exhaust valve closes in Comfort mode to reduce cabin noise. Coding the ASDM module to permanently disable the valve closure keeps the full exhaust sound in every mode, without touching the hardware. Two approaches covered: BimmerCode standard mode and E-Sys FDL.
? How the S55 Exhaust Valve Works
The S55 engine uses an electronically controlled exhaust valve (flap) in the rear muffler section. In Comfort mode, the valve is held closed — routing exhaust through the muffler's baffles for a quieter, more subdued tone. In Sport and Sport+ modes, the valve opens to allow more direct flow, creating the characteristic M3/M4 crackle and volume.
Many owners want the valve open in all modes — particularly those who start the car in a garage or neighborhood in Comfort but still want the full sound. This coding change tells the ASDM (Active Sound Design Module) to keep the valve open regardless of driving mode.
Affects noise in residential areas. An always-open exhaust flap on a stock S55 is noticeably louder at idle and low speed. Think about where you park before committing to this change. It's easy to revert, but you'll want to know that going in.
✓ Before You Start
- F80 M3 Sedan (2014–2018), F82 M4 Coupe (2014–2018), or F83 M4 Convertible (2014–2018) — S55 engine only
- BimmerCode app (iOS/Android) — OR — E-Sys software with ENET cable
- Compatible OBD2 adapter: Veepeak OBDCheck BLE (BimmerCode) or ENET cable for ENET-based F-series coding
- Verify your exhaust is stock or that your aftermarket system has a functioning valve — some aftermarket exhausts remove the valve entirely, making this coding irrelevant
- BimmerCode backup saved before making any changes
→ Coding Procedure
BimmerCode exposes a simplified exhaust valve option in the ASDM module. It's the cleanest path and has the least risk of inadvertently touching other parameters. The module may be labeled ASDM or Active Sound Design in your car's module list.
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Connect BimmerCode and go to Expert Mode
Connect your OBD2 adapter. Open BimmerCode, connect to the F80/F82/F83. Tap Expert Mode.
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Select the ASDM module
In the Expert Mode module list, locate ASDM (Active Sound Design Module). Tap it and read coding data. On some F8x builds it may also appear under MSDM or the module list may just label it by its part number — look for the exhaust-related module.
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Find the exhaust valve control parameter
Within the ASDM CAFD, look for exhaust valve/flap control. The parameter name varies by ASDM hardware version, but common patterns include:
Parameter Set To Default Notes KLAPPENSTEUERUNG_AKTIV nicht_aktiv aktiv Disables valve closing logic — flap stays open verify in your ASDM EXHAUST_VALVE_CONTROL permanent_open auto Direct "always open" flag on some ASDM revisions verify These parameter names must be verified against your specific ASDM version. The S55 ASDM has multiple hardware revisions across the 2014–2018 production run. The exact parameter label differs between them. When you read the ASDM module in BimmerCode Expert Mode, search for parameters containing "KLAPP" (flap), "VALVE", or "SOUND" — one of those will be the valve control. Do not assume the parameter name without reading your actual module data first.
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Code the change
Once you've identified the correct parameter, set it to the always-open value and tap Code. After a successful write, do an ignition cycle.
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Verify across driving modes
Start the car and listen. Then switch between Comfort, Sport, and Sport+ modes. With a successful coding change, the exhaust note should remain consistent (open valve sound) across all modes — no longer closing down in Comfort. The difference is most obvious at idle and light throttle.
E-Sys gives direct FDL access. Useful if BimmerCode doesn't expose the ASDM module on your specific build, or if you want to cross-reference the raw CAFD structure.
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Connect via ENET and read FA/SVT
Connect the ENET cable to the OBD2 port and to your laptop. Open E-Sys. Establish a connection, then read FA (Vehicle Order) and SVT (System Vehicle Type) using Connection → Read FA and Read SVT.
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Select the ASDM module and read coding data
In the SVT tree, find ASDM. Right-click → Read Coding Data. This generates a .ncd CAFD file in the E-Sys working directory.
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Open the FDL editor
Expand the generated CAFD folder in E-Sys. Right-click the .ncd file → Edit FDL. Search for exhaust/flap-related parameters (search "KLAPP" or "VALVE").
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Set the valve control to always-open state
Identify the exhaust valve parameter (same search as the BimmerCode method). Set the Werte (value) to the always-open state — typically 00 for disabled/nicht_aktiv, or a specific "open" mode code. Save the FDL.
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Code the module
Back in E-Sys, right-click the ASDM module → Code. Wait for the confirmation. Perform a full ignition cycle after coding completes.
⚡ Alternative: Hardware Valve Controller
If coding alone doesn't fully achieve your goal — or if your ASDM revision doesn't expose the right parameter — a dedicated exhaust valve controller module is a clean hardware alternative.
These modules plug in-line with the valve's OEM connector and intercept the ECU signal. Options include:
| Product | Control method | Notes |
|---|---|---|
| Aulitzky Exhaust Flap Controller (S55) | Steering wheel buttons (hold M1/M2 to open/close) | Plug-and-play, fully reversible |
| xHP Flashtool (Stage 2+) | Transmission/DME tune-based valve logic | More comprehensive tune; adds other performance changes |
Hardware controllers don't require coding and are immune to software updates reverting the change. CodeWerk doesn't endorse specific products — do your own research before purchasing.
! Risks & How to Revert
ASDM is a 3/5 difficulty for good reason. Unlike FEM_BODY brightness parameters, the ASDM interfaces with the exhaust valve actuator. Setting an incorrect parameter could cause the valve to behave erratically or cause a check engine light. Read your actual ASDM module data before coding — don't rely solely on parameter names documented here.
Do not touch DME (engine ECU) parameters. Some older forum guides suggest modifying DME parameters for exhaust flap control on the S55. This carries significant risk. The ASDM route is the correct approach. Leave DME parameters alone unless you are working with a qualified tuner who knows your specific ECU revision.
To revert: Open BimmerCode → Expert Mode → ASDM → Restore Backup. The valve returns to its original mode-dependent behavior on the next ignition cycle.
If a check engine light appears after coding: Restore the ASDM backup immediately. Clear the fault code with BimmerCode or a scan tool. If the light returns after clearing, there's a hardware issue (stuck valve, actuator problem) that's unrelated to the coding and needs physical inspection.