Weird P0420 come/go code. (1 Viewer)

[MH_Stevens]

For some time I have a P0420 left bank (with the VSC and TRAC lights on) and not been able to identify an issue. Occasionally when on the freeway the lights would clear but come back with a cold start. Now the check engine etc lights have gone for good but the OBD meter still shows the P0420 code.

So far the warnings have not come back and the code has not cleared after a few days driving.
I have two questions:

The shop put in new plugs before this started so might a bad plug job be likely?
Is it a good idea to replace the O2 sensors anyway after 225,000 miles even when static data looks good and cat has a 70F temp increase? I have had associated increase in fuel consumption.
Regards,

 

[saucebox]

I don't know about the temp increase, more knowledgeable people can maybe talk to that.

But there really isn't a good reason not to replace the O2 sensors in the back. It's an easy job (unless you have Slee skids ), and they're about $45 each for the replacements on Amazon. I got Denso 234-4154 to replace the ones on my MY03, direct fit (no wiring, just plug it in and run).

 

[MH_Stevens]

OK thanks a bundle. Is it two or four sensors to change?

 

[looking4lc]

my p0430 issue was fuel pump being dirty, might consider replacing it if it has not been replaced.

 

[white_lx]

.... the lights would clear but come back with a cold start.

Before changing any O2 sensors, make sure you don't have a tiny exhaust/manifold leak in front of the rear O2 sensors. A cracked manifold or small exhaust leak that closes up when warmed up can cause these symptoms.

 

[saucebox]

OK thanks a bundle. Is it two or four sensors to change?

I only changed the two rear sensors on mine. Similar circumstances, except my code was for the other side (0430). Intermittent at first, then eventually became kind of semi-permanent.