Effective, January 1, 2013 a number of revisions were made to the automated photo enforcement laws in the California Vehicle and Evidence Code, for the purposes of trying to remedy defects which were declared in numerous California appellate court rulings during the previous five years. Consequently, most of the appellate cases are considered overruled at this time, and the process of trying to defeat photo red light tickets in California must be repeated, because the case law that prevented most of the enforcement has now been nullified by the later legislative enactments.
At this time, absent some new challenge, if you fail to appear and answer the complaint, a warrant for failure to appear will issue against you from the court, which is a misdemeanor
with a $1,000 fine
and up to one year jail, and you will have to explain to the judge why you never appeared, in addition to having to fight the underlying ticket.
The ticket is valid and enforceable, though, someone may again come along with another successful appeal, and things may turn around again.
Hope this helps.