I recently replaced the plugs with new OEM plugs and my check engine light came back on after about an hour with a P420 code. Can anyone help with diagnosis and remedy? Thanks. The car is a 1998 and seems to be running perfectly...so im scratching my head on this because before there were only random misfire codes.

 

look for an exhaust leak on bank 1...

 

+1
at the outlet flange on the cat most likely.
VERY common on out cars

 

yup. exhaust leak
I have it right now.
exhaust shop is charging 2 bills to weld a new pipe and O2 sensor plug

 

wayyyyyy too much.

 

I know
I wanna go where vincent went to get his exhaust done but it's a bit of a drive from me

 

The same issue happened to my 2000 a couple weeks ago. As PD said, it was a exhaust leak at the flange coming of the collector on the passenger side. Has a O2 sensor like two inches downstream of it that the leak was messing with.

The muffler guy, Carline here in Calgary, gave me two options. 1) He could pull it all apart and fix it for a couple hundred or 2) just MIG the flange around its circumference!

His thinking was that if it needs to be worked on later the weld is shallow enough that it can be easily ground away with out taking very little flange material. Easy decision from where I sat!

I reset the OBD2 using my TORQ application and it has not come back.

The best part of the fix was the cost! $0.00.

Good guy...

 

error code table: http://www.spobd2.com/service/diagno...wnload-38.html