TCU tuning
GM 5L40E TCU tuning: the Siemens GS20
The GM 5L40E and its Siemens GS20 control unit are the gearbox almost nobody tunes. We do. The GS20 is calibrated by hand from your own read: shift times, shift pressures and scheduling, the delays taken out and a manual mode that holds the gear, so a six-cylinder BMW automatic finally shifts like it means it.
Supported
What is covered.
| Gearbox | Variants | Control unit | Fitted to | How it is read |
|---|---|---|---|---|
| GM 5L40E | 5L40E | Siemens GS20 | BMW six-cylinder automatics of the E46, E39 and E53 X5 era | With Bimmertuningtools QuickFlash, or with our own flashing solution: ask support or email us for access. |
Calibrated by hand
Tuned to how you want it to shift.
Every TCU file is written by the tuner from your own read. Tell us how the car should feel, and anything in this list, or anything else you ask for, is set to match.
Shift times
Quicker, firmer changes, or smoother ones if that is what the car is for.
Shift pressures
Clutch pressures raised to match the torque the engine now makes, so the gearbox holds it instead of slipping.
Shift scheduling
When it changes up and down, in every mode, moved to suit the engine and how you drive.
Torque limits
The internal TCU torque limits removed, so a tuned engine is not cut back by the gearbox.
Unnecessary delays
The hesitation built into kickdown, downshifts and pulling away taken out.
True manual mode
In manual mode it holds the gear you chose and does not change up on its own at the limiter.
- Read with Bimmertuningtools QuickFlash, or with our own flashing solution. For access to ours, open a support ticket from your account or email info@remapify.net.
- Autotuner and Magic Motorsport Flex do not read the GS20 as far as we know, so check your tool before you book the car in.
- The GS20 is a specialty: there are no off-the-shelf files for it. Every one we do is calibrated for that car.
Questions
Before you order.
Can the 5L40E GS20 TCU be tuned?
Yes. We tune the Siemens GS20 that controls the GM 5L40E in BMWs, and calibrate it by hand from your own read. There are no ready-made files for this unit, which is exactly why it is worth doing properly.
How do I read a GS20 TCU?
With Bimmertuningtools QuickFlash, or with our own flashing solution. For access to ours, open a support ticket from your account or email info@remapify.net. As far as we know, Autotuner and Magic Motorsport Flex do not read the GS20. Upload the read when you order, and the tuned file is written back with the same tool.
Is the 5L40E the same as the ZF gearboxes?
No. The 5L40E is a General Motors five-speed with a Siemens GS20 control unit, used by BMW alongside its ZF automatics. It needs its own calibration work, and we do it.
Do I need a TCU tune if my ECU is remapped?
It is not required, even with a Stage 2 remap, but it is recommended whenever the ECU is tuned. The gearbox control unit has its own torque limits and shift pressures set for the standard engine. A TCU tune removes those limits and raises the pressures, so the gearbox holds the extra torque and shifts the way the car now needs to.
Can the gearbox be tuned on a car with a standard ECU?
Yes. A TCU tune does not need any change to the engine ECU. Plenty of people only want the gearbox to shift faster, hold gears in manual mode or lose the delays, and that is done entirely in the TCU.
Is the TCU file custom or off the shelf?
Custom. Every TCU file is calibrated by hand by the tuner, from your own read, to how you want your transmission to feel. Gearbox work is never automated and never delivered from a library. Say in the order what you want, such as firmer shifts, a comfortable daily or a true manual mode, and the calibration is written around it.
How do I order a TCU tune?
Read the TCU with your tool, then submit it through your account like any other file: pick your vehicle, upload the read and choose the gearbox solution. Describe how you want the transmission to behave in the order notes or the job thread, and the tuner will ask if anything is unclear. Creating an account is free, and every account is reviewed before it is activated.
What does a TCU tune cost?
The price is shown inside your account, in the price list and on the order form, because it is read live from the catalogue. Jobs are paid for with credits bought by card through Stripe.
Send us your TCU read.
Order it like any other file: pick your vehicle, upload the read and choose the gearbox solution.
Other gearboxes: ZF 8HP, ZF 6HP, Mercedes 722.6, VAG (DSG, S tronic), ZF 8HP in other makes