Malfunction Indicator Lamp - GMC 2009 Yukon XL Owner's Manual

When the Light Flashes First and Then is
On Steady
This indicates that there could be a problem with the Tire
Pressure Monitor System. The light flashes for about a
minute and stays on steady for the remainder of the
ignition cycle. This sequence repeats with every ignition
cycle. See Tire Pressure Monitor System on page 5-71
for more information.

Malfunction Indicator Lamp

Check Engine Light
A computer system called OBD II (On-Board
Diagnostics-Second Generation) monitors operation
of the fuel, ignition, and emission control systems.
It ensures that emissions are at acceptable levels for
the life of the vehicle, helping to produce a cleaner
environment.
3-44
If the check engine light comes on and stays on, while
the engine is running, this indicates that there is an
OBD II problem and service is required.
Malfunctions often are indicated by the system before
any problem is apparent. Being aware of the light
can prevent more serious damage to the vehicle.
This system assists the service technician in correctly
diagnosing any malfunction.
Notice: If the vehicle is continually driven with this
light on, after a while, the emission controls
might not work as well, the vehicle's fuel economy
might not be as good, and the engine might not
run as smoothly. This could lead to costly repairs
that might not be covered by the vehicle warranty.
This light should come on
when the ignition is on, but
the engine is not running,
as a check to show it
is working. If it does not,
have the vehicle serviced
by your dealer/retailer.