GMC SIERRA 2020 Owner's Manual page 139

138 Instruments and Controls
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
costly repairs not covered by the
vehicle warranty. This could also
affect the vehicle s ability to pass
an Emissions Inspection/
Maintenance test. See
Accessories and Modifications
0 329.
If the light is flashing : A
malfunction has been detected that
could damage the emission control
system and increase vehicle
emissions. Diagnosis and service
may be required.
To help prevent damage, reduce
vehicle speed and avoid hard
accelerations and uphill grades.
If towing a trailer, reduce the
amount of cargo being hauled as
soon as possible.
If the light continues to flash, find a
safe place to park. Turn the vehicle
off and wait at least 10 seconds
before restarting the engine. If the
light is still flashing, follow the
previous guidelines and see your
dealer for service as soon as
possible.
If the light is on steady : A
malfunction has been detected.
Diagnosis and service may be
required.
Check the following:
If fuel has been added to the
vehicle using the capless funnel
adapter, make sure that it has
been removed. See Filling the
Tank with a Portable Gas Can
under Filling the Tank (Pickup
Model) 0 283 or
Filling the Tank (Chassis Cab
Model) 0 285. The diagnostic
system can detect if the adapter
has been left installed in the
vehicle, allowing fuel to
evaporate into the atmosphere.
A few driving trips with the
adapter removed may turn off
the light.
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
Recommended Fuel (Except
6.2L V8 Engine) 0 280 or
Recommended Fuel (6.2L
V8 Engine) 0 281.
If the light remains on, see your
dealer.
Emissions Inspection and
Maintenance Programs
If the vehicle requires an Emissions
Inspection/Maintenance test, the
test equipment will likely connect to
the vehicle's Data Link
Connector (DLC).