Circuit/System Description
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The TBCM runs this diagnostics to check whether there is a fault on the internal TBCM 5-volt references used to monitor the User Gain switch circuits. This diagnostics checks if the circuits 5-volt references is within a range for normal operation.