Diagnostics
OnStar Vehicle Diagnostics will perform a vehicle check every month. It will check the engine, transmission, antilock brakes, and major vehicle systems.
It also checks the tire pressures, if the vehicle is equipped with the Tire Pressure Monitoring System.
If a diagnostics check is needed between e-mails, push 
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Advisor can run a check.
See also:
Antilock Brake System (ABS) Warning Light
For vehicles with the Antilock Brake System (ABS), this light comes on
briefly when the engine is started.
If the light does not come on, have it fixed so it will be ready to warn if
there is ...
Trans (Transmission) Temp (Temperature) (CTS-V Only)
This display shows the transmission
fluid temperature in either degrees
Celsius (°C) or degrees
Fahrenheit (°F). ...
Trunk Release
The remote trunk release button
is on the driver door, inside the
storage compartment under the
armrest.
Vehicles with an automatic
transmission, the shift lever must
be in P (Park) or N ...