2003 Pontiac Bonneville Owner's Manual - Page 290

If No Steam Is Coming From Your Engine If you get an engine overheat warning but see or hear no steam, the problem may not be too serious. Sometimes the engine can get a little too hot when you: Climb a long hill on a hot day. Stop after high-speed driving. Idle for long periods in traffic. Tow a trailer. If you no longer have the overheat warning, you can drive. Just to be safe, drive slower for about 10 minutes. If the warning doesn't come back on, you can drive normally. If the warning continues and you have not stopped, pull over, stop, and park your vehicle right away. If there's still no sign of steam, you can idle the engine for three minutes while you're parked. If you still have the warning, turn off the engine and get everyone out of the vehicle until it cools down. You may decide not to lift the hood but to get service help right away. If you get the overheat warning with no sign of steam, try this for a minute or so: 1. In heavy traffic, let the engine idle in NEUTRAL (N) while stopped. If it is safe to do so, pull off the road, shift to PARK (P) or NEUTRAL (N) and let the engine idle. 2. Turn on your heater to full hot at the highest fan speed and open the window as necessary. 5-31