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:
How to Check Lubricant
To get an accurate reading, the vehicle should be on a level surface.
For Two-Wheel-Drive vehicles, the proper level is from 15mm to 40mm (0.6
in to 1.6 in) below the bottom of the filler plu ...
Brake Adjustment
Every time the brakes are applied,
with or without the vehicle moving,
the brakes adjust for wear. ...
Making a Call
Radio with CD
1. Press the PHONE button twice.
2. Enter the character sequence.
See “Entering a Character Sequence” in Operation for more information.
3. Select Call to start dialing the numbe ...