Changes to technical characteristics

Yes. Any change to the technical characteristics recorded on the registration certificate — converting a motorcycle’s power output, changing the number of seats, an ethanol (E85) conversion, and so on — must be declared and the carte grise updated. The work must be done or certified by an approved professional, and you will need their attestation to support the application. Driving with a carte grise that no longer matches the vehicle can invalidate your insurance.

Changes that affect official vehicle data: number of seats, flex-fuel / E85 conversion, power or body type changes, motorhome conversion, and any work requiring approval or an attestation from an authorised body or professional. If in doubt, check whether the new characteristic already appears on your certificate.

Typically: the current carte grise, ID, proof of address, the attestation from the professional who carried out or approved the modification, and any approval documents. Cerfa 13750 and a mandate are also required if you use an accredited professional.

When the conversion is done correctly and must be recorded on the certificate, yes: the update makes the fuel system official for the administration and your insurer. Keep the approved installer’s attestation — it is the central document in the file.

At a roadside check, a mismatch between the vehicle and the carte grise can mean a fine and immobilisation. More importantly, the insurer may refuse to cover a claim if the vehicle was modified without updating the certificate. Declaring the change protects you legally and financially.

The cost depends on the type of modification and the taxes that apply (sometimes a fixed administrative fee, sometimes a recalculation linked to the new characteristics), plus any professional service fee. Ask for a quote once we have reviewed your technical attestation.

Yes, as soon as you have the required technical attestations. Upload the documents through our online flow; we check consistency and submit the request to update the registration certificate.