BMW Siemens MS43 · MS43X-Custom-Firmware (ms4x)
MS43X map switch
Three complete calibration sets, switched with the pedals
- Choose ECU
- Check file
- Pay
- Download
What the patch does
The patch places a second and third calibration set in the free flash of your MS43X and hooks into 18 map accesses and 16 constant reads of the firmware. Slot 1 stays untouched — exactly the calibration the file arrived with, your risk-free way back. Slots 2 and 3 start as copies of it and are calibrated by you in TunerPro.
The three slots
Stock / fallback
Unchanged: the calibration you uploaded. After flashing, the car drives exactly as it did before.
Stage 1
Starts as a copy of slot 1. Your everyday setting — ignition, lambda, boost and limiter all freely calibratable.
Stage 2
A second free set. Typically for E85, track use, or a valet setting with reduced power.
Switchable per slot
- Full-load ignition — RON98 and E85 separately
- Lambda/AFR targets — RON98 and E85 separately
- VANOS targets, intake and exhaust
- Boost: target (RON98/E85), pilot PWM, fixed PWM
- Launch control: on/off, rpm, ignition offset, AFR target
- Rolling antilag: ignition offset for RON98 and E85
- Overboost and scramble boost: threshold, hysteresis, offset
- Rev limiter including hysteresis
- Idle speed — standard, driving, A/C, driving + A/C
- Overrun cut: cut-off rpm, antilag rpm, minimum ignition
- Injection time correction curve
What you need
- The file must be stock — as it left the factory: no tune, no stage, no catalyst or DPF removal, no patched-in launch control, ignition cut or pops code. EWS-off is allowed.
- It must be a fresh full read from your own car, complete and including the bootloader section. A partial read without that section is not enough.
- No bins from the internet. Files from MS4X, forums, collections or file swaps are not supported — they come from a different vehicle, are often already modified, and will not work on your ECU.
- An MS4x tool to correct the checksum and write the full flash — the shop deliberately does not calculate the checksum.
- TunerPro to calibrate slots 2 and 3.
Specifications
Questions about this product
How do I switch slots in the car?
Only while stationary with the engine off and the ignition on. Press and hold the brake — the tachometer needle jumps to the active slot, showing the switch is armed. Release the brake, then fully press and release the throttle once: that steps one slot further, 1000 rpm = slot 1, 2000 = slot 2, 3000 = slot 3. Pressing the brake again ends the input; after a few seconds without input it ends by itself. The thresholds and timings are parameters in the XDF.
Why does the file have to be stock?
The patch identifies the firmware by fixed byte patterns and writes into areas that are empty in stock files. An existing tune has changed those patterns and may have occupied those areas. The check rejects such files rather than quietly overwriting something — that would be the shortest path to a dead ECU.
Why does slot 1 stay unchanged?
So there is always a state in which the car runs on exactly the calibration it had before flashing. Anyone testing a new calibration puts it in slot 2 or 3 and can switch back while stationary, without flashing.
Can I pass the file on to a friend?
No. Every file is created for exactly one vehicle and only runs there. A second car needs a second purchase — which is what the price is calculated for.
Does the shop calculate the checksum?
No, deliberately not. The bin leaves the shop uncorrected; you fix the checksum with the MS4x tool you also flash with. That keeps exactly one tool responsible for the last step, with no two versions of the truth.
What does an update cost?
Nothing. Simply upload your bin again: the shop recognises you and releases the download without payment.
Can I undo this?
Yes, by flashing back your saved original file. That is exactly why a verified full read before the first flash is mandatory.