Negative response code 0x21 indicates that the controller is temporarily busy. It should be interpreted with the operation underway and the approved retry behaviour.

What to check next

Check whether another diagnostic operation is still active and review the tool log for the preceding step. Allow the supported software to manage timing instead of repeatedly sending commands. If the response persists, investigate the session and connection before assuming internal ECU damage.

Useful information for an enquiry

Send the task being attempted and a log covering the events before the busy response.

An immediate repeated click is not always a useful retry. Follow the manufacturer’s process for that operation.

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.