GMC 2003 C4C042 Owner's Manual page 101

If Your Diesel Engine Won't Start
If you've run out of fuel, look at "Running Out of Fuel."
See "Diesel Fuel Requirements and Fuel System" in
the Index.
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.
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If your batteries don't have enough charge to start your
engine, see "Battery" in the owner's manual.
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 "Diesel Fuel Requirements and
Fuel System" in the Index.
If the engine starts, runs a short time, then stops, your
vehicle needs service.
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.