Quad drivers are power integrated circuits typically used to drive
solenoids, relays, etc.  They were manufactured by, IIRC, Allegro
Semiconductor, Inc. for GM products.  The early versions weren't
short-circuit protected; hence, you read in shop manuals from the
1980s/early 1990s to replace the ECM if a short is found in, for
instance, the idle air control motor (replace IAC motor and ECM).

Later QDMs are short-circuit protected and monitor the output to see
whether a commanded electrical signal (logic 0 or logic 1 -- power, of
course) actually occurred.

I do not know the details of the problem, below.  The DTC suggests
either a short or an open in the driven circuit.  If the owner doesn't
have access to a factory shop manual, something like Mitchell's
ON-DEMAND will be useful (it's often available at public libraries).

Hope this helps,

Bohdan