GMC 2003 GMT560 T-Series Owner's Manual page 129

The TCS may operate on dry roads under some
conditions. When this happens, you may notice a
reduction in acceleration. This is normal and doesn't
mean there's a problem with your vehicle. Examples of
these conditions include a hard acceleration in a
turn, an abrupt upshift or downshift of the transmission
or driving on rough roads.
When the light in the top of the TCS button is on, the
TCS is off and will not limit wheel spin. Adjust your
driving accordingly.
The light in the top of the TCS button will come on if the
TCS is turned off by pressing the TCS on/off button.
The light may also come on if a problem has been
detected in either the traction control system or
the anti-lock brake system.
The traction control system automatically comes 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
traction control system off if you ever need to. You
should turn the system off if your vehicle ever gets stuck
in sand, mud or snow and rocking the vehicle is
required. See Rocking Your Vehicle To Get it Out under
If You Are Stuck: In Sand, Mud, Ice or Snow on
page 4-30 .
If you used the TCS button to turn the system off, the
light in the top of the button will come on and stay
on. You can turn the TCS back on at any time by
pressing the button again; the light should go off.
To turn the system on or
off, press the traction
control button located in
the instrument panel
switchbank.
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