Pontiac 2004 GTO - Manual (Page 220)

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,
with the parking brake applied, shift to PARK (P)
or NEUTRAL (N) and let the engine idle while
you get out and check that the cooling fan is
working.
2. If the fan is working and the temperature gauge
needle has not returned to its normal position
within a few minutes, stop the engine and remove
the ignition key.
Look for leaks at the radiator hoses and
connections, heater hoses and connections,
radiator, and water pump. Be careful when checking
these areas as they will probably still be hot. If
you find a major leak or other problems that may
have caused the engine to overheat, do not run the
engine until these problems have been corrected.
If you do not find anything wrong, you should check
the engine coolant level. See Engine Coolant on
page 5-25. You should also check the air intake
area below the front bumper to ensure that it is clear
of leaves and road grime.
3. Turn off your air conditioning and 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.
You may decide not to lift the hood but to get service
help right away.
5-30