GM Service Manual Online
For 1990-2009 cars only

The rear wiper/washer switch, when in LO, activates the wiper automatically in a delay mode. When in HI, the wiper operates continuously. Pressing the rear wiper/washer WASH button while the switch is in HI position activates the washer pump. When the WASH button is pressed while the wiper/washer switch is in the LO position, the wiper function changes from delay to continuous operation while the WASH button is held and continues for approximately three wipe cycles after the WASH button is released.