Per California's smog check inspection procedure and guidelines, (available
at
http://www.bar.ca.gov/80_BARResources/ftp/pdfdocs/Smog_Check_Procedures.pdf)
the Check Engine Light or Malfunction Indicator Lamp inspection needs to be
conducted after the emissions and visual portions of the smog check.
Contrary to the guidelines we have information that State BAR Inspectors
have started allowing smog check technicians who notice a customer's check
engine light being on or illuminated before the smog inspection, to warn the
customer that his or her vehicle will fail the smog inspection, strictly as
a matter of good business and customer relations. This practice is still
against state smog check guidelines, and some smog stations still choose to
inspect vehicles as they are driven in to their shops, check engine light on
or off.
To answer your question... Legally smog technicians have an obligation to
inspect the check engine light after the smog inspection has started, and
after completing the emissions and visual parts of the test, with no
requirement to advise the vehicle owner of the potential failure.
