Just looked for a thread on this, to no avail. A poster has had this problem (bank 1 lean) and was suggested to swap O2 sensors. I have done that and the lean bank problem didn't follow the O2 sensor. The question is what to check next?
Also how does one check the O2 sensor behind the cat?

TIA

 

MAF sensor

 

The O2 sensor behind the converter only measures it's efficiency, not lean or rich.

Since the code is for Bank 1 only I would suspect a leak in the intake or exhaust manifold for Bank 1 (IIRC are cyls 1,2,3).

 

Hum, MAF sensor, that I can clean. Thanks bhuffstutter

rla2005, Since i dont have any exhaust noise would you suggest to reseal the intake? or throttle body

 

Good read about the P0420 code...

The Misleading Nature of the PO42O Code - Eastern Manufacturing

 

Good catch! I knew I should have verified the code definition

OP: P0420 indicates the PCM thinks the converter efficiency is below a preset threshold, not a lean condition.

Good read in the link above.

 

Yes, that is a good read. Have seen it before, which has lead me down this path. Next step is to get some MAF cleaner. And to find a buddy with a scope so I can check out the wave forms. Next time the light comes on i will post the the numbers. (it takes about two weeks for it to come on). Living 1 and a half miles from work doesn't help either.

 

Any updates? Did you manage to fix your issue?

 

I have been riding the bike. Not the truck much. I went to the Houston autorama Sunday and the cel came on. Going to get the code read this weekend.

 

Well got some time to look at the truck. I think the rear O2 sensor was the wrong one. So I have replaced it. When i went and cleared the light the data shot showed about 2200 rpm and 67mph which means i was in 4th and on the gas. I might be off on the rpm a touch. we shall see what happens

 

I want to update my experience with the P0420 code.

My P0420 code would show up every about 100 miles or so after I reset the code. It showed up after I removed the distributor to get better access to the lifter galley cover to replace the gasket.

Although I marked the distributor with my sharpie, I didn't use a timing light to check my timing. My fuel trims got pretty high, which made me think that my timing was off. After a two weeks of resetting codes, I took it to a mechanic to check the timing. Turns out it was off by 2 degrees.

First drive after the timing reset and I get the P0420 code again. I figured I needed a set of O2 sensors. I ordered a set, but never got around to installing them (got busy and it got cold). After about 3 weeks of resetting the codes, I noticed that the P0420 code has now gone away on its own.

I suspect that I should have pulled the battery cable off to reset the engine computer's long term fuel trim values. I think that they were causing the computer to set the P0420 code. I think that the code has gone away now because the long term fuel trim has now averaged back to normal.

 

On a long trip, after a 150 miles or so. I replace the rear O2 sensor about a month ago and that fixed it. Haven't had the cel come on and it runs like a new truck.