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MaxxECU online help

The BMW DCT CAN protocol is not yet released, still under testings and development.

BMW DCT related links

BMW DCT Wiring information.


BMW INPA diagnostic tool.

BMW DCT error codes.

BMW DCT TCU firmware flashing.

DCT clutch relearn.

MTune - DCT Settings.

MTune - DCT Control.

DCT Realtime Data description.

DCT hardware upgrade.


Will be updated when released!




DCT settings


Gearbox type

Specifies the gearbox type and the TCU (Transmission Control Unit) used. The actual TCU version is the most important thing here.

BMW GS7D36SG (with BMW 335 TCU)

BMW GS7D36SG (with BMW M3 TCU)

Note: BMW M4 DCT support will probably be available later in 2020 (if there is demand for it, let us know).


Shifter type

Specifies which gear shifter is used.

OEM BMW shifter - with this option, stock shifter, SPORT button (BMW 335) or drivelogic button (BMW M3) must be present and communicate directly with the TCU.

Note: later on, there might be support to run this solution without the stock shifter...(if there is demand for it, let us know).


Shift hardness

Specifies the shift hardness source.

Drivelogic/sport button - use the M3 drivelogic button, or the 335 SPORT button for shifting hardness.


Shiftcut source

Specifies which function to trigger the MaxxECU shiftcut input.

torque request from tcu - Uses the torque request input to trigger the internal shiftcut input (preferable use this method).

shift signal from tcu - Uses the shift input (which happends a few milliseconds before the above actual torque request signal) as shiftcut input trigger.

Note: The reason why we have this option, is because we have seen issues with the above Torque request from TCU signal from the TCU in some application (for an unknown reason).




The above image is an example of how the different signals MaxxECU is receiving during an up shift event from a M3 TCU, and also how it should look like!

1. The shift signal is received (Green).

2. Gear indication (Blue) will increment during the up shift event.

3. The Torque reduction signal sends a signal to the MaxxECU indicating to lower engine torque (shiftcut) during the shift operation.



How to determine the Shiftcut source


Multiple torque reduction signals in one single shift operation


If you get the above, several torque reduction signals during one single up shift event, you cannot use torque request from tcu as the shiftcut source. You have to use shift signal from tcu as shiftcut source.

Note: Currently we dont know what is causing this, but abviously the TCU is unhappy with some torque value does not match a calculated value inside the TCU, read more on how we control the TCU.



Lack of torque reduction signal randomly


In the above example, we get a very short, or not even an Torque reduction Request signal at all, in the above case, you must use shift signal from tcu as shiftcut source.





Shiftcut delay time when using the shiftcut signal from TCU as shiftcut source.


Note: If using the Shift signal from TCU as shiftcut source, an shiftcut delay of around ~0.040sek (40msec) is nesseccary to make torque reduction at the correct time.



TCU speed source

The vehicle speed source we report to the TCU.

MaxxECU vehicle speed (TCU OEM rear end diff ratio used) - Can ONLY be used when your rear end diff ratio is 3.15 for the M3 TCU and 2.65 for the 335 TCU.

MaxxECU vehicle speed (using rear end diff ratio setting) - Uses the correct vehicle speed(undriven) and your rear end diff ratio to calculate a correct speed value for your vehicle to the TCU.

simulated (using RPM and current gear) (experimental) - Experimental setting if a proper TCU control can be made without a vehicle speed sensor.

Note: The 4 speed values we send to the TCU has a direct relation to shifting points, performance and clutch slippage during shift operations. Therefore the vehicle speed inside MaxxECU must be very precise.