2007 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 134

Ignition Positions With the key in the ignition switch, you can turn it to four different positions. A (LOCK): This position locks your ignition when the key is removed. The steering locks when equipped with a manual transmission. It is a theft-deterrent feature. You will only be able to remove your key when the ignition is turned to LOCK. B (ACCESSORY): This position allows you to use things like the radio, power windows and the windshield wipers when the engine is off. {CAUTION: On manual transmission vehicles, turning the key to LOCK will lock the steering column and result in a loss of ability to steer the vehicle. This could cause a collision. If you need to turn the engine off while the vehicle is moving, turn the key only to ACCESSORY. Do not press the key release button while the vehicle is moving. Notice: Using a tool to force the key from the ignition switch could cause damage or break the key. Use the correct key and turn the key only with your hand. Make sure the key is all the way in. If it is, turn the steering wheel left and right while you turn the key hard. If none of this works, then your vehicle needs service. 134