2006 g35x P2A03/P2A00 after changing downstream o2 sensors

[si2ki30]

I was getting P0420/430 DTC codes (cant remember which side), so I replaced both downstream o2 sensors with A-Premium sensors from Amazon.

The P0420/430 codes went away.

Now, I was getting P2A03(b2s1) and P2A00(b1s1) for both the upstream A/F sensors. I tried all the relearning procedures and used injector cleaners/fuel cleaner, etc.

Still getting P2A03/00

The upstream sensors are harder to get to, so I avoided touching them for a while.

Just replaced the driver side upstream A/F sensor (b2s1) with Denso 234-4302, cleared codes, but then after a little while P2A03 came back for this side, as well as P2A00 for the passenger side (still using old sensor)/00.

I've never had the intake taken apart and I checked for intake leaks with a smoke tool, and havent found any.

Any ideas?

[VStar650CL]

The front sensors are 1.5V widebands, I have a hard time imagining one of them went bad just as you changed the rear O2's. The ECM does use the rears as a feedback check for the fronts, so I'd say your new bank1 rear is probably crappy.

[si2ki30]

The front sensors are 1.5V widebands, I have a hard time imagining one of them went bad just as you changed the rear O2's. The ECM does use the rears as a feedback check for the fronts, so I'd say your new bank1 rear is probably crappy.

Just put in an order for a Denso left downstream sensor, will report back when installed.