Circuit/System Verification
WARNING: This page is about a different car, the 2008 GMC Yukon and 2008 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
Ignition ON, observe the scan tool MAP and BARO sensor parameters. The readings should be within 5 kPa of each other, and also the current BARO for your location. Refer to Altitude Versus Barometric Pressure .