GMC 2001 Sierra - Manual (Page 176)

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The TRACTION OFF light may come on for the
following reasons:
D If you turn the system off by pressing the TAS on/off
button the light will come on and stay on. To turn the
system back on, press the button again; the light
should go off.
D If you move the shift lever to FIRST (1), the light
will come on and stay on to indicate that the Traction
Assist System is off. This is normal operation. To
turn the system back on, move the shift lever back to
a position other than FIRST (1); the light should go
off. See “Traction Assist System” in the Index.
D The light will come on and stay on if the TAS automatic
engagement feature has been turned off. To turn the
system on, press the TAS off/on button; the light should
go off. To turn the automatic engagement feature back
on, see “Traction Assist System” in the Index.
D If the Traction Assist System is affected by an
anti - lock brake system, Traction Assist System or
engine - related problem, the system will turn off and
the light will come on. Have your vehicle serviced.
D If the vehicle is driven over an extremely rough road,
the system will turn off and the light will come on.
The light will go off a few seconds after the rough
road conditions go away or when the vehicle comes
to a complete stop. This is normal operation.
Malfunction Indicator Lamp (Service
Engine Soon Light in the United States or
Check Engine Light in Canada)
United States Canada
Your vehicle is equipped with a computer which monitors
operation of the fuel, ignition and emission control systems.
This system is called OBD II (On - Board
Diagnostics - Second Generation) and is intended to assure
that emissions are at acceptable levels for the life of the
vehicle, helping to produce a cleaner environment. The
SERVICE ENGINE SOON or CHECK ENGINE light
comes on to indicate that there is a problem and service
is required. Malfunctions often will be indicated by the
system before any problem is apparent. This may prevent
more serious damage to your vehicle. This system is also
designed to assist your service technician in correctly
diagnosing any malfunction.