07 chevy avalanche keyless entry system acts like it falls asleep.WHY??? on 2007 Chevrolet Avalanche

after exiting the vehicle the factory keyless remote will lock/unlock and start,30 seconds goes by and the system becomes faulty,nothing works,until you unlock the door with the key the system will work for another 30 seconds or so..please help

2 answers
have the anti theft module codes scanned and post so we can adv
possible anti-theft module issue...recommend dealership