2003 GMC Sierra 1500 Pickup Owner's Manual - Page 137

Running Your Engine While You Are Parked It's better not to park with the engine running. But if you ever have to, here are some things to know. Also, idling in a closed-in place can let deadly carbon monoxide (CO) into your vehicleeven if the fan is at the highest setting. One place this can happen is a garage. Exhaust - with CO - can come in easily. NEVER park in a garage with the engine running. Another closed-in place can be a blizzard. See "Winter Driving" in the Index. Idling the engine with the climate control system off could allow dangerous exhaust into your vehicle. See the earlier Caution under "Engine Exhaust." CAUTION: (Continued) I 2-50