Chevrolet/GMC 3.0L Duramax Diesel Engine Supplement (GMNA-Localizing-
U.S./Canada-13336148) - 2020 - CRC - 9/5/19
10
Instruments and Controls
Malfunction Indicator
Lamp (Check Engine
Light)
This light is part of the vehicle
’
s
emission control on-board
diagnostic system. If this light is on
while the engine is running, a
malfunction has been detected and
the vehicle may require service. The
light should come on to show that it
is working when the ignition is on
with the engine not running. See
“
Ignition Positions
”
in the owner
’
s
manual.
This light may also come on when
the system has detected a problem
with the Diesel Exhaust Fluid (DEF)
management system. See
.
Malfunctions are often indicated by
the system before any problem is
noticeable. Being aware of the light
and seeking service promptly when
it comes on may prevent damage.
Caution
If the vehicle is driven continually
with this light on, the emission
control system may not work as
well, the fuel economy may be
lower, and the vehicle may not
run smoothly. This could lead to
costly repairs that might not be
covered by the vehicle warranty.
Caution
Modifications to the engine,
transmission, exhaust, intake,
or fuel system, or the use of
replacement tires that do not
meet the original tire
specifications, can cause this light
to come on. This could lead to
(Continued)
Caution (Continued)
costly repairs not covered by the
vehicle warranty. This could also
affect the vehicle
’
s ability to pass
an Emissions Inspection/
Maintenance test. See
When the light is on, a malfunction
has been detected. Diagnosis and
service may be required.
Poor fuel quality can cause
inefficient engine operation and poor
driveability, which may go away
once the engine is warmed up.
If this occurs, change the fuel brand.
It may require at least one full tank
of the proper fuel to turn the light off.
See
.
If the light remains on, see your
dealer.