Every 2-3 tanks of gas, my "check emission system" light comes on and the code that comes up is P0420. I went to get the car inspected yesterday and the light was not on. It failed. The gas cap was good. No code came up. But the two faults were Heated 02: Not Ready and Evap Sys: Not Ready. I should also mention that when the check emission light comes on, I'll disconnect the battery and it resets. It had been about a week since I last did that and performed the inspection yesterday. I'm not a mechanic and am not familiar with car or technical terms, but I would like some advice from anyone who might have experience with this issue. I don't want to spend hundreds just trying to diagnose the issue then have to shell out whatever it costs to fix it on top of that. I understand it might not be a straight forward one-answer fix. But as much insight as I can get on this problem would be helpful. Thanks!