I have a 2006 Pathfinder with ~54K miles on it. Recently the SES light came on and the code pulled was P2A00. OBD2 data scanning showed A/F bank 1 sensor 1 reading of ~0.3V and not changing much. If I raise the RPM to 3-4K range for a few seconds then release the petal completely, it raises the reading to ~0.8V for a short time before returning to ~0.3V. Under the same conditions A/F bank 2 sensor 2 reads ~0.61V rising to ~ 1.3V when rev'd and released, so while it seams that the sensors are doing something, they are clearly not reading the same. I followed all of the code resolution steps in the FSM but I found no problems, so per the FSM I replaced the A/F bank 1 sensor 1 with a new Bosch direct fit sensor. Unfortunately this produced no change in the readings, even after driving the vehicle ~110 stressful highway miles over a mountain pass. I then swapped the old "bad" sensor into the bank 2 sensor 1 slot and what do you know, it reads fine in that slot. I checked the harness for problems the best I could according to the FSM and found nothing so I'm not sure what else is left except the ECM. This is very expensive and so I'd like to be sure before I do this any help would be greatly appreciated.

Maybe the catalytic converter is bad.

Also, at least for our R50s, the ECU needs a reflash or reprogram of some sort to upgrade the ECU firmware? May apply to your 2006.

Based on the information I've seen it doesn't seem likely that the cat is bad as the primary job of "sensor 2" is to monitor the cat and I have recieved no codes for that. I've tried to find out if a reflash is necessary for this truck from the dealer but they seem confused by the question. I told them I replaced the O2 "sensor 1" and asked if I needed a reflash and they asked me what update I wanted, so it did not seem that they were aware of one for this particular model. At this point I have replaced both bank 1 sensor 1 and and bank 2 sensor 1 now but still no change: bank 1 reads ~0.3V and bank 2 still reads ~0.6V. It does not seem to be affected by which specific sensor is in which bank. I have driven hundreds of miles at this point and while the SES light has remained off there is now a recent code pending again (P2A00). I need to take a very long trip (2K miles) at the end of this week and I'm not sure what to try next. I did find a Titan forum with a post with the same problem (0.3V on one side and 0.6V on the other) but they received no response, at least in the forum.

It looks like NTB08-103a - 2007 FRONTIER, PATHFINDER, XTERRA; DTC P0031, P0051, P0133, P0153, P2A00, P2A03, P1148, P1168 would apply to your vehicle, but you have a 2006. I don't see any other TSBs relating to P2A00, but I'll check for any more which may have reflashes as part of the procedure.

Thanks, I had not seen that one, probably since it is listed under 2007. I will check my old sensors to see which ones I have and talk to my dealer to see if they think this may also be a problem on mine. Somehow I doubt they will want to do the reprogram on a 2006 when the TSB says 2007, they will probably be afraid that it will not be compatible and may cause more problems but I will see.