reconnect your OBDII code reader to see if all conditioner have been met. I/M Readiness.
I found this on the web, it explains the process…hope it’s correct.The drive cycle can be difficult to follow exactly under normal driving conditions. Thus, it is better to drive it in restricted area!

1. The universal OBD-II drive cycle begins with a cold start. You should have coolant temperature below 50 C/122 F, and the coolant and air temperatures within 11 degrees of one another. This condition can be achieved by letting the car to sit overnight.
   
2. The ignition key must not be left ON position before the cold start. Otherwise the heated oxygen sensor diagnostic may not run.
   
3. Start the engine and idle the engine in drive for two and half minutes, with the A/C and rear defroster on if equipped.
   
4. Turn the A/C and rear defroster off, and speed up to 90 km/h (55 mph) under moderate, constant acceleration. Hold at a steady speed for three minutes.
   
5. Slow down to 30 km/h (20 mph) without braking. Do not depress the clutch if you are running with manual transmission.
   
6. Speed up back to 90-100 km/h (55-60 mph) at 3/4 throttle. Hold at a steady speed for five minutes.
   
7. Slow down to a stop without braking.
   

 

@Y2K_Frenzy just curious, did the Check Engine Light ever return?

 

Well fellas I think I’m going to call this one fixed. It’s been 100 miles or so and the CEL hasn’t came back on. I believe in my case P0420 was caused by a cruddy IAC o-ring. I figured (and hoped) it might be based on my 1+1 usually equals two theory. I recently took it off to clean and the light came on shortly after. That and I drove it 700 miles home when I bought it without a CEL (prior to cleaning IAC of course).