GMC 2003 GMT560 T-Series Owner's Manual page 47

When the engine coolant temperature is below 149°F
(65°C) and the outside temperature is below 50°F
(10°C), the exhaust restrictor will come on within
45 seconds of starting the engine. After running the
engine for an additional 45 seconds, the engine idle will
increase.
The exhaust restrictor will shut off and engine idle will
return to normal once the engine is warmed up, or
the transmission is shifted into range.
If Your Engine Won't Start
If you're not out of fuel, and your engine won't start, do
this:
Turn your ignition key to RUN. Immediately after the
wait to start light goes off, turn the ignition key to
START.
If the light doesn't go off, wait a few seconds, then try
starting your engine again. And, see your dealer as soon
as you can for a starting system check.
If the light comes on and then goes off and you know
your batteries are charged, but your engine still
won't start, your vehicle needs service.
If the light does not come on when the engine is cold,
your vehicle needs service.
If your batteries don't have enough charge to start your
engine, see Battery on page 5-34 for more information.
Be sure you have the right oil for your engine, and
that you've changed the oil at the proper times. If you
use the wrong oil, your engine may be harder to start.
Be sure you are using the proper fuel for existing
weather conditions. See What Fuel to Use on page 5-5 .
If the engine starts, runs a short time, then stops,
your vehicle needs service.
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CAUTION:
Do not use gasoline or starting "aids" such as
ether, in the air intake. They could damage
your engine. There could also be a fire, which
could cause serious personal injury.
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