Owner’s Manual

Black plate (21,1)
GMC Yukon/Yukon XL Owner Manual - 2011
Instruments and Controls 5-21
Malfunction
Indicator Lamp
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.
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.
If the malfunction indicator lamp
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 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.
Notice: Modifications made
to the engine, transmission,
exhaust, intake, or fuel system
of the vehicle or the replacement
of the original tires with other
than those of the same Tire
Performance Criteria (TPC) can
affect the vehicle's emission
controls and can cause this light
to come on. Modifications to
these systems could lead to
costly repairs not covered
by the vehicle warranty. This
could also result in a failure
to pass a required Emission
Inspection/Maintenance test. See
Accessories and Modifications on
page 10‑3.
This light comes on during a
malfunction in one of two ways:
Light Flashing: A misfire
condition has been detected.
A misfire increases vehicle
emissions and could damage the
emission control system on the
vehicle. Diagnosis and service
might be required.