For 1990-2009 cars

Scan Tool Output Control | Additional Menu Selection(s) | Description
--- | --- | ---
HVAC Fan Auto On | Outputs | When On is selected with the scan tool, the body control module (BCM) supplies a ground for coil of the ignition 3 relay (IGN 3) in the underhood bussed electrical center (UBEC), which supplies battery power to the blower motor and the HVAC control assembly. The blower motor switch must be in a speed position other than OFF for output to function. When OFF is selected with the scan tool, the BCM removes the ground for the IGN 3 relay and the blower motor is disabled.