Quad driver 4 - The quad driver is located inside the PCM. The quad driver consists of four separate electronic switches used by the PCM to energize verious solenoids and relays.
The PCM checks the condition of the quad driver switch output and displays either LOW (switch is on) or HIGH (switch is off).
Note that this display is indicating the actual condition of the switch output and NOT the command given to the switch by the PCM.
DTC P1670 - Driver 4
Linky linky: http://www.troublecodes.net/articles/quaddriver.shtml