GM Service Manual Online
For 1990-2009 cars only

The vehicle has an automatic transmission shift lock control system. You have to apply the brake pedal then press the shift lever button before you can shift from P (Park). See Automatic Transmission Operation.

If you cannot shift out of P (Park), ease pressure on the shift lever and push the shift lever all the way into P (Park) as you maintain brake application. Then press the shift lever button and move the shift lever into the gear you wish.