I have a CAT CT660S. I have an active code of 3490-3. It is saying the after treatment purge valve is shorted to power. The coil on the purge valve seems to be getting powered all of the time. However I have checked resistance and continuity on the coil wires all the way back to the ACM and everything seems to be checking out. The ACM powers the purge valve, so I am unsure on what direction to head next. Anyone out there have this problem before?