Cooling System - Chevrolet 2004 Impala Owner's Manual

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.
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, 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. Also, see
"Overheated Engine Protection Operating Mode" listed
previously in this section.
You may decide not to lift the hood but to get service
help right away.
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Cooling System

When you decide it's safe to lift the hood, here's what
you'll see:
3400 V6 Engine
A. Engine Coolant Recovery Tank
B. Electric Engine Cooling Fans
C. Radiator Pressure Cap