At a glance
What can fail
The HVAC controller's software can become temporarily overloaded by multiple data inputs, causing it to send incorrect signals to the heater mode door. This makes the door move to wrong positions during heating, and repeated movement may damage the mode door shaft over time.
What the fix does
The dealer will replace the HVAC controller assembly, inspect the mode-door shaft for damage, and repair or replace it if needed.
Summarized — see the official notice for exact wording, dates, and contacts.