My g has 107,000 miles and last week I finally decided to put some Lucas Fuel Injector Cleaner in the fuel. After an hour of driving the the SES light came on. Ran the codes and got the P0455. The light stayed on for a few more days and around a 1/3 of tank it turned off. However, this evening the light came back on. Again P0455. Is this behavior known? Is it an artifact of the fuel injector cleaner?

 

That code usually is just from a loose fuel Cap.

Also Lucas is garbage, if you want something that works and you can get it locally, Redline Si-1

 

^+1 on Lucas, I have always used BG 44k,

 

Following the lead of several different forum post and the advice of the dealer I changed the gas cap. However after 150 miles of driving today the light still hasn't turned off. Should I reset the SES or wait and see if it goes off?

 

You must erase the code for it to go away. It was probably just loose no need to change it out. Reset the light and make sure the cap is tight.

 

Look into your evap purge valve, apply the 12v to see if it clicks.

If you dont know what or how to do this, just bring it to someone. Because the gas cap fix is almost NEVER a valid one. Once in a blue moon you find someone who completely forgot to close the cap or maybe cross threaded it but i've never found the case. Its either the purge valve not closing or some vacuum lines. Its not a easy fix to do, unless you want to throw parts at it and guess.