The replacement unit communicates, but warning lamps remain and P1647 is stored. At this stage, more trial-and-error coding can make the history harder to untangle. Save the current report and establish exactly what changed.
The Ross-Tech VAG reference describes P1647, 18055 or 005703 as a request to check coding of ECUs on the powertrain data bus. Incorrect or incomplete coding of related controllers is listed as a cause. Its detailed examples apply to specified Audi brake-electronics systems, so the instructions should not be copied into an unrelated car. P1647 technical reference.
Gather the before-and-after information
- Original and replacement hardware numbers, including suffixes.
- Software identities and any saved coding or configuration records.
- A full scan from before the work, if one exists, plus the current scan.
- The reason for replacement and the exact operations already attempted.
If a module was already missing when the car arrived, say so. If a previous file is labelled “original” but its provenance is unknown, preserve it and explain that uncertainty. Clear records are more valuable than a confident label that cannot be verified.
Define the intended outcome
For a programming enquiry, state whether the aim is to restore the factory configuration after repair, complete a replacement procedure or diagnose a new warning. Compatibility, authorised access and the correct vehicle procedure need confirming before a session is promised.
Discuss ECU coding with AXION. Workshops can send the diagnostic package ahead of an arranged visit. Our UK-wide electronics page explains the distinction between suitable postal modules and work that needs the vehicle.
Reviewed September 2026. Use the complete manufacturer-specific fault description and vehicle repair information.