Hi All,

I had the stupid code p0420. So I seafoamed, cleaned the EGR port both per the DYI's and changed the EGR and bank 1 O2 sensor in that order over the last 2 weeks. The 02 had some serious carbon on it so I changed it 3 days ago (about 45 miles). The check engine light came on again today with the same code. Should I change the second 02 sensor? Any suggestions?

Thanks

 

420 is usually the rear 02 or the cat. What 02 did you buy? one from the dealer or one from a parts store?

 

I bought a bosch from the autoparts store. Is there a way to test the cat?

 

Bosch. Many have had issues with those in the past. But like i said before, that code is usually the rear O2 or the cat. There isnt a way you can test the cat, but muffler shops usually can.

 

Try running a can of bg44k in a quarter tank of gas. Do some wide open throttle accelerations and a highway cruise around 2000 rpm for 15 - 20 minutes. {use d4 if nec} You might have to repeat this process, but if two times don't do it, I don't think more will help.
As fasttyms said, convertors and o2 sensors are typical culprits. If you have to have it diagnosed, make it clear you expect a guarantee if the light comes back on. The reason I say this is that aftermarket catalytic convertors are not 100% on this. If you can get one that is certified for sale in california, you get a better guarantee, and a better probability of keeping the light out. Probably the cheapest "fix" that's close to 100% is to use a spark plug non-fouler on the rear o2 sensor.[pretty sure it's illegal, but you'd smog just fine if no visual inspection]

 

OK. So I had the check engine reset. I drove for about 100 miles and the car passed inspection. The only thing I did was run a full tank of shell v-power.

Thanks for all your help

 

just to let you know i used a bosch o2 sensor and it was crap so i choked the money and bought one from the dealer. it hurts a little but its alot better

 

Bosch usually, at least use to, makes good stuff, but something about their O2 sensors. I use to have a Dodge Daytona and those cars also had problems with Bosch O2 sensors.

 

Yes. Your code P0420 is specific to your catalytic converter efficiency dropping below threshold. Why would you look anywhere else? I fix these regularly by.....replacing the catalytic converter.