Chevrolet 2010 Tahoe Owner's Manual page 260

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.
4-40
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.
This light comes on during a malfunction in one of
two ways:
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.
To prevent more serious damage to the vehicle:
Reduce vehicle speed.
Avoid hard accelerations.
Avoid steep uphill grades.
If towing a trailer, reduce the amount of cargo
being hauled as soon as it is possible.