Well after a month or more of chasing this CEL issue for an 02 sensor it has come down to an exhaust leak. A small exhaust leak. Could not hear it under normal driving or when at idle. But when coming off a standing stop with 3/4 throttle you could hear a different sound coming from the exhaust which turned out to be a very small exhaust leak!
Fixed that and no issues since.

 

Interesting, congrats ! Where was the exhaust leak located?

 

Truck has OEM exhaust manifolds. The connection at the exhaust manifold to the Y pipe is where there was an issue. Either I did not torque the bolts correctly or after putting 800 miles on it those bolts had become a bit loose. Torqued them down & no more problem.

 

Thanks for posting all the info, ive been dealing with similar issues in my 04 1500 QC 4.7L. Replaced motor w 0 mi remanufactured, 4 new mopar 02 sensors, coils, plugs, exhaust, pcm flashed to vin, fuel pump to injectors replaced, the list goes on
First start up - 02 heater sens codes, both banks sensor 1. Codes changed to voltage high and rich condition. No heater circuit code.
swapped 02 sensors - same codes. 2.5v at signal wire. Engine off key on/run. ???? Too high? Freeze frame and live data showing same. Ugh..
3 weeks ago brought to dealer to find and fix wiring issue, even replace harness. None available. They repaired old, found a few breaks. Installed and started, same p0135, p0155 - rich condition both banks and high voltage (if memory is correct, i dont recall high voltage code)
Picking up truck tomorrow, still same codes as when i dropped it off and $1200 to start over...
. Will start by torquing exhaust from manifolds back, see if that helps. Any ideas? Even the dealer cant fix this one, im at wits end.

 

I fought the 02 sensor issues for about 800 miles on the new engine.
Installed new Denso sensors on both banks upstream & still pulled 02 codes! Kept clearing the codes. I would pull a code after I put 50 miles on truck. Finally I checked tthe exhaust & found the bolts slighly loose at the exhaust manifold & Y pipe. Retorqued them & to date no issue.

Have you pulled plugs and checked them visually for any issues?

 

Not yet, although that is the plan if the exhaust does not solve the issue. I had thought that since everything was new it should be fine - i am due for the 1,000 mi break-in oil change and will check them to be sure there are no defective new parts then. Swapping sensors did not change codes, why i figured it was a wiring issue.
One point i should mention, according to mopar and vin, the sensors for up and downstream were different, yet connectors were the same. After modifying connectors i installed new, then tried the old and same codes. Puzzled on that one and no answer from dealership.

 

About the plugs. What I am asking is if you pulled one plug from each cyl and visully looked at the to see if they are firing normaly. Are they soot covered, etc. They all should have a normal tan color, if not than the cyl they came from has an issue.

Also 02 sensors are the same for up stream or down stream, plus the downstream just informs you that the cat is bad if it throws a code, at least thats what I found out.

And if you do any work yourself check out Rock Auto for parts. If you can't find a part there check Parts Geeks.

 

Glad you got it fixed. If you're ever running down exhaust leaks again, there is a simple way to find them. While idling, have someone stop up the tailpipe with a rag. The leaks will hiss.