97 Elantra and Code P0455

I have a 97 Hyundai Elantra with a 1.8 DOHC motor with 150K miles on
it. I am getting ODB2 error code P0455 and the check light is on. I
am using a carchip from davisnet.com to read the codes. I have reset
the light once but it came back on in like three days or so, about 100
miles or so. I had the car in for the gas cap recall and they replaced
the cap. I think that was like 30 or 40 K miles ago? The car appears
to run about the same as it ever has.

Should I just get another cap? What else would cause this code.

Thanks for your time/help with this.

 

This code means that the car cannot vacuum the evap system during its self
test. This can be caused one of two ways, either by a leak (such as a
missing/loose/defective fuel cap) or by preventing the vacuum from
reaching the tank and sensor (possibly due to stuck closed purge valve or
other blockage).

 

Used the shop manual and checked the purge valve. The valve resistance
reads good and moves when voltage is applied. Don't know if voltage is
getting to valve?

When should I see voltage to valve? Still need to check overall vac
off motor. Also need to see how much new flue cap from dealer is.

Thanks for the help so far.