97 yukon:turning the key in the ignition used to lock the door locks automaticaly now it does'nt work.Any ideas?

i'm pretty sure auto door locking/unlocking wasn't a factory option until the restyle in 2000. does your yukon have an aftermarket security system or alarm?

nope,no aftermarket alarm.any ideas

check you owners manual. if you recently disconnected your battery it could have turned off the lock feature. look in the manual under power door locks or so.