GM Service Manual Online
For 1990-2009 cars only

Your vehicle has an automatic transmission shift lock control system which locks the shift lever in PARK (P) when the ignition is in the LOCK. Apply your regular brakes before shifting from PARK (P) when the ignition is in RUN. See Automatic Transmission Operation .

If you cannot shift out of PARK (P), ease pressure on the shift lever and push the shift lever all the way up into PARK (P) as the brake application is maintained. Move the shift lever into another gear.