GMC 2003 C4C042 Owner's Manual page 99

Starting Your DURAMAX
Diesel Engine
Your diesel engine starts differently than a
gasoline engine.
Automatic Transmission
Move your shift lever to PARK (P) or NEUTRAL (N).
Your engine won't start in any other position
a safety feature. To restart when you're already moving,
use NEUTRAL (N) only.
NOTICE:
Don't try to shift to PARK (P) if your vehicle is
moving. If you do, you could damage the
transmission. Shift to PARK (P) only when your
vehicle is stopped.
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t
Manual Transmission
Move your shift lever to neutral and hold the clutch
pedal to the floor while starting the engine. Your vehicle
won't start if the clutch pedal is not all the way
down
Starting Your Engine
1. Turn your ignition key to RUN.
--
that's
Observe the wait to start light. See "Wait To Start
Light" in the Index. (This light may not come on
if the engine is hot.)
2. As soon as the wait to start light goes off,
IMMEDIATELY turn the ignition key to START.
When the engine starts, let go of the key.
NOTICE:
Holding your key in START for longer than
15 seconds at a time will cause your battery to be
drained much sooner. And the excessive heat can
damage your starter motor.
--
that's a safety feature.