Crennel, who was sacked by the Browns in December 2008 after going 24-40 during four seasons with Cleveland, spent last year recovering from hip replacement surgery.
"That breath has filled my lungs, my enthusiasm is up, my energy is up," he added. "My hip, there's no pain in it, so I feel really good about being able to come in and trying to help build this program."
"At the present time, the opportunity is to be the defensive coordinator for the Chiefs and that is what I am putting all of my energy into."
(Writing by Mark Lamport-Stokes in Los Angeles; Editing by Nick Mulvenney)