0420 code

External Since: Mar 22, 2004 Posts: 85

96 Silverado, 305, man trans, 133k miles

Ok, I replaced both O2 sensors in on the left side. I did not replace
the after cat one. I cleared the codes and the 0420 code came back. This
code is supposed to be cat efficiency. I cleared it again yesterday and
it has not come back.....yet. Why did I get this code after replacing
the sensors? Is the after cat sensor getting ready to go? Should I
replace it anyhow?

Thanx
Mike

External Since: Jul 28, 2004 Posts: 513

the 'cat efficiency' code relates to O2 seen in the exhaust AFTER the CC

I'd replace that one too, if you already did the other two

"Mike Copeland" <mcopeland.TakeThisOut@REMOVETHISpobox.com> wrote in message
news:419b64ee_1@news1.prserv.net...
> 96 Silverado, 305, man trans, 133k miles
>
> Ok, I replaced both O2 sensors in on the left side. I did not replace
> the after cat one. I cleared the codes and the 0420 code came back. This
> code is supposed to be cat efficiency. I cleared it again yesterday and
> it has not come back.....yet. Why did I get this code after replacing
> the sensors? Is the after cat sensor getting ready to go? Should I
> replace it anyhow?
>
> Thanx
> Mike