2004 GMC Sierra 1500 Pickup Owner's Manual - Page 116

Ignition Positions With the key in the ignition switch, you can turn it to four different positions. {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 OFF. Do not press the key release button while the vehicle is moving. Notice: If your key seems stuck in LOCK and you can not 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. 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. C (RUN): This is the position for driving. D (START): This position starts your engine. 2-22