On the BMW M54 Siemens MS43, checksum correction is not a single calculation over a whole file. MS4X's MS43 reference describes three CRC16 checks and two 32-bit additive checks associated with system-monitoring parameters. The stored monitoring sums are themselves inside CRC-protected regions, making correction order significant.
Memory and check locations
These are full-image offsets from the cited MS4X reference. Check the software and layout of the image in hand; a storage address is not by itself a complete description of a checksum's input ranges or parameters.
| Check | Documented storage location | Purpose as described by MS4X |
|---|---|---|
| Boot CRC16 | 0x3C24 | Boot section |
| Program CRC16 | 0x6FDE0 | Program section |
| Calibration CRC16 | 0x73FE0 | Calibration section |
| Program 32-bit addition | 0x6FDAE | Program system-monitoring parameters |
| Calibration 32-bit addition | 0x72FFC | Calibration system-monitoring parameters |
The cited source describes a 512 KiB full flash with calibration at 0x70000–0x7FFFF inclusive. In an unwrapped, contiguous 64 KiB calibration-only slice beginning at 0x70000, subtract 0x70000: the calibration monitoring-check location maps to partial offset 0x2FFC, and the calibration CRC location maps to 0x3FE0. Verify the writer's actual file convention before using that mapping. Program and boot locations are outside this slice.
Why the order matters
Suppose a calibration edit changes a byte included in the calibration monitoring sum. The existing value at 0x72FFC may no longer match. A matching algorithm first calculates and stores the new monitoring sum. That writes bytes within the calibration CRC-protected area. The calibration CRC must therefore be calculated from the final data after that inner sum has been updated. If the CRC is calculated first and the monitoring sum is changed afterwards, the outer CRC may no longer match. MS4X explicitly describes this dependency.
This is an illustrative dependency, not a claim that every map lies in the monitoring sum or that every edit changes both checks. The actual covered ranges, byte order, initial conditions and any other affected checks must come from a matching, documented implementation. The locations alone are insufficient to calculate the numerical results.
Practical workflow
- Identify the MS43 software and preserve the original full read and any separate calibration read. Confirm whether the file is a raw full image or calibration-only slice.
- Check the original with a tool documented for the exact image and retain the report. If an original fails, establish why before correcting it.
- Edit a copy, identify the affected regions, and use a supported checksum implementation. Where applicable, update the monitoring additions before their enclosing CRCs. Inspect the final file and recheck it.
- Determine whether the writing tool changes checks during programming. MS4x Flasher documentation describes on-the-fly and local-file correction for its supported controllers. Confirm the actual version, method and scope used.
- Save the edit comparison, tool report and corrected output. Verify the ECU's response and the programmed software through the appropriate diagnostic and readback workflow.
The source cautions that the calibration monitoring checksum is associated with drive-by-wire monitoring. Preserving these integrity checks is preferable to assuming they are redundant. A checksum pass is not evidence that a changed calibration is sensible or that every part of the image was verified.
Source: MS4X contributors, Siemens MS43 and MS4x Flasher. Offset arithmetic and workflow are editorial interpretation, not hardware verification; checked 10 November 2026.