A recent tire change from stock to 20-inch wheels on a T6.1 Volkswagen Transporter presented a challenge when attempting to adjust the speedometer coding using VCDS. While changing the tire diameter coding via the “Variant” setting in module 17 (Instruments) is possible, reverting to a smaller diameter proved problematic. This article outlines the issue, the resulting errors, and potential solutions for correcting the coding.
The Challenge of Reverting Tire Diameter Coding
Historically, adjusting the speedometer for different tire sizes in Volkswagen vehicles was achieved through “K-Number” coding. In the T6.1, this has been replaced with a numerically based “Variant” setting (1-8 or 0-8). In this instance, after increasing the “Variant” value to accommodate the larger 20-inch wheels, an attempt to revert to a lower value resulted in a “Coding Rejected Error 22: Conditions Not correct or Request Sequence Error.” This error persisted even when attempting the change using ODIS online with genuine VAS6154 and GeKo access. Disconnecting the battery, a common troubleshooting step, did not resolve the issue and introduced additional errors.
Resulting Errors and Symptoms
The failed coding attempts led to a malfunctioning Adaptive Cruise Control (ACC) system. The ACC ceased to function in gears 5 and 6, while operating normally in gears 1-4. This behavior mirrors a known issue in earlier T5.1/T6 models associated with specific “K-Number” settings, where the gear selection indicator in the Driver Information System (DIS) displayed incorrectly for gears 5 and 6.
Potential Solutions for Correcting “Variant” Coding
The core question remains: how to successfully change the “Variant” coding back to the correct value in module 17. Several possibilities are being explored:
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Identifying Dependencies: It’s suspected that other control modules, potentially related to the transmission or ESP, may need adjustments before the “Variant” coding in module 17 can be reverted. Further investigation into coding dependencies is necessary.
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Software Updates: Outdated software in related modules could contribute to coding conflicts. Checking for and applying the latest software updates to the vehicle’s control modules might resolve the issue.
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Factory Reset: While disconnecting the battery didn’t help, a more comprehensive factory reset of the relevant modules might be necessary. This procedure would require specialized equipment and should be performed by a qualified technician.
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Dealer Intervention: If all else fails, consulting with a Volkswagen dealership equipped with the latest diagnostic tools and access to factory resources might be the only solution.
Pre and Post Coding Autoscans
The following autoscans were performed before and after the coding changes, highlighting the differences and new fault codes that appeared:
Pre-Coding Autoscan
Post-Coding Autoscan
Analyzing these scans reveals a significant increase in fault codes across various modules following the attempted coding change. The appearance of errors in the engine (01), ABS brakes (03), park/steer assist (10), and auto distance regulation (13) modules suggests a broader impact than just the instrument cluster.
Conclusion
Changing tire diameter using VCDS in the T6.1 Volkswagen Transporter requires caution. While increasing the “Variant” value seems straightforward, reverting to a lower value can lead to unexpected errors and system malfunctions. Thoroughly researching coding dependencies and potential software updates is crucial before attempting any modifications. If difficulties arise, seeking professional assistance from a qualified technician or Volkswagen dealership is recommended. Further investigation and testing are ongoing to identify a definitive solution to this specific coding challenge.
