DTC P0634-4B: PCM/ECM/TCM Internal Temperature A Too High - Over temperature: Action

WARNING: This page is about a different car, the 2015 Jaguar XK, 2014 Jaguar XK, 2013 Jaguar XK, and 2012 Jaguar XK. However, it is still accessible from the selected car via links, so may be relevant.

Clear the DTC. With the ignition off, wait 10 minutes and re-check DTC
Check the engine control module does not have additional external covering or obstructions which may cause overheating
Check and install a new engine control module as required. Refer to the warranty policy and procedures manual, or determine if any prior approval program is in operation, prior to the installation of a new module/component