2004 GMC Sierra 1500 Pickup Owner's Manual - Page 181

To idle an automatic transmission equipped vehicle with the DRL off, set the parking brake. Shifting the transmission into PARK (P) will also allow you to idle the vehicle with the DRL off. The DRL will stay off until you release the parking brake or shift the transmission out of PARK (P). To idle a manual transmission equipped vehicle with the DRL off, set the parking brake. The DRL will stay off until you release the parking brake. Your parking lamps and/or low-beam headlamps must be on for your fog lamps to work. Press the button to turn the fog lamps on. Press the button again to turn them off. An indicator light will glow in the button when the fog lamps are on. Remember, fog lamps alone will not give off as much light as your headlamps. Never use the fog lamps in the dark without turning on the headlamps. The fog lamps will go off whenever the high-beam headlamps come on. When the high beams go off, the fog lamps will come on again. The fog lamps will be cancelled after the ignition is turned off. If you still want to use the fog lamps after you restart the vehicle, you will need to press the fog lamp button again. Fog Lamps If your vehicle has fog lamps, use them for better vision in foggy or misty conditions. The fog lamp button is located on the left side of your instrument panel. 3-17