GMC 2002 Envoy - Manual (Page 234)

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The TRAC OFF light on the button will come on under
the following conditions:
D The Traction Assist System is turned off, either by
pressing the TAS on/off button or turning off the
automatic engagement feature of the TAS.
D The transmission is in FIRST (1); TAS will not
operate in this gear. This is normal.
D The vehicle is driven on an extremely rough road.
When the vehicle leaves the rough surface, slows
down or stops, the light will go off and TAS will be
on again. This is normal.
D A Traction Assist System, Anti - Lock Brake System
or engine - related problem has been detected and the
vehicle needs service.
The Traction Assist System, as delivered from the
factory, will automatically come on whenever you start
your vehicle. To limit wheel spin, especially in slippery
road conditions, you should always leave the system on.
But you can turn the TAS off if you ever need to. You
should turn the TAS off if your vehicle ever gets stuck in
sand, mud or snow and rocking the vehicle is required.
See “Rocking Your Vehicle” in the Index.
To turn the system on
or off press the TAS
on/off button located
near the shift lever.
If you used the button
to turn the system off,
the TRAC OFF light
on the button will
come on and stay on.
You can turn the system back on at any time by pressing
the button again. The TRAC OFF light on the button
should go off.
If desired, you can change the TAS automatic
engagement feature so that the system will not come on
automatically when the engine is started. To do so:
1. Park the vehicle with the ignition off and the
transmission in PARK (P).
2. Turn the ignition to RUN; do not start the engine.