Negative response code 0x7E means the requested subfunction is not supported in the current diagnostic session. Communication with the ECU can be healthy while that operation remains unavailable.

What to check next

Check whether the authorised tool entered and maintained the required session. Review the preceding log for a timeout, reset or session change. Correct vehicle selection and supported procedure matter before any internal module fault is suspected.

Useful information for an enquiry

Send the operation name and the response sequence from the start of the session.

Do not confuse session access with permission to bypass protected functions. Use the appropriate authorised diagnostic workflow.

Speak to AXION

For module programming and coding support, send your vehicle details and fault report. Workshop assessment is in Didcot, Oxfordshire. Suitable postal or remote work is confirmed before booking.

Technical background from py-uds. The referenced design explains the principle; the vehicle-specific procedure determines the repair.