GMC 2003 C4C042 Owner's Manual page 98

Exhaust Restrictor (Diesel Engines)
(If Equipped)
If your vehicle is equipped with this feature, there is an
exhaust restrictor valve located in the exhaust stream.
The valve closes to provide back pressure to the engine
for the purpose of warming the engine quickly.
The exhaust restrictor operates:
D
while the engine is running.
D
while the vehicle is not moving.
D
while the accelerator, brake and clutch pedals are
not pressed.
D
while idling or driving in cold temperatures.
D
when the shift lever is in NEUTRAL (N)
or PARK (P).
On vehicles equipped with a diesel engine exhaust
brake, the exhaust brake switch must be on. The
indicator in the exhaust brake switch will be lit when the
exhaust restrictor is active. The exhaust brake indicator
light in the center of the instrument panel will also be lit
whenever the exhaust restrictor is active.
When the engine coolant temperature is below 149
_
(65 C) and the outside temperature is below 50
_
(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.
_
F
_
F
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