2005 GMC Sierra 1500 Pickup Owner's Manual - Page 112

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. C (Run): This is the position for driving. D (Start): This position starts your engine. Notice: If your key seems stuck in LOCK and you cannot turn it, be sure you are using the correct key; if so, is it all the way in? Turn the key only with your hand. Using a tool to force it could break the key or the ignition switch. If none of these works, then your vehicle needs service. 2-22