The CVN, or Calibration Verification Number, is a digital signature (often a 4-byte checksum) generated by the manufacturer to verify that the engine control unit (ECU) software is genuine and unmodified. Each time a calibration is performed, the CVN is recalculated and stored in the ECU. During diagnostics, this number is read by diagnostic tools to confirm whether the ECU software matches the original factory version.
When an ECU is remapped (chiptuning, EGR delete, AdBlue delete, etc.), the CVN may change, which triggers alerts during OEM diagnostic checks. The CVN Patch allows the recalculation or preservation of the original CVN so that the ECU remains compliant and undetectable, even after tuning.
Dealerships can read the CVN with any diagnostic scanner. If the CVN does not match the expected value, the system can raise alerts, such as the well-known "TD1" code in the VAG Group, flagging unauthorized modifications even if the ECU has been restored to stock.
The CVN Patch ensures the ECU keeps an original-like number, passing manufacturer diagnostic checks.
With a CVN Patch, even dealer diagnostic tools (VW, Audi, BMW, Mercedes, etc.) will not detect the remap.
A remap with CVN Patch provides more security against warranty inspections from dealerships.
While the CVN Patch hides modifications, any ECU tuning remains illegal for road use if it alters emissions or Euro 6 compliance.
Without a CVN Patch, dealerships can detect ECU modifications. This may lead to warranty refusal, fault codes such as TD1, or issues during official inspections.
Yes, most modern vehicles with ECUs use CVN as a compliance check. It is widely implemented across VAG, BMW, Mercedes, Ford, Land Rover and more.
The CVN Patch remains active as long as the ECU retains the tuned file. After dealer updates or new writes, it may need to be reapplied.
The CVN Patch (Calibration Verification Number) is a key step to keep ECU remapping undetectable to manufacturer tools. The CVN acts as a digital fingerprint that reveals if the ECU software has been altered. Without patching, dealerships can detect modifications and void warranties, even after restoring the stock file. With a CVN Patch, tuning professionals ensure compliance, discretion and reliability for their clients. This service is essential to avoid codes such as TD1 in Audi/VW and to preserve the integrity of modern ECUs.
Join our platform and benefit from a professional, discreet and reliable CVN Patch service to protect your remaps and maintain ECU compliance.
