After getting the dreaded P1273 code (which relates to A/F lean condition in bank 1 upstream) I replaced all O2 Sensors (up and downstream) and plugs. Still no joy.

After cleaning the MAF sensor, checking for exhaust and vacuum leaks, replacing the air filter, having the computer relearn, and even trying a different manufacturer's upstream sensors, I still couldn't get rid of the 1273 code.

Finally, I broke down and took it to a local respected independent shop and explained what I'd done. I left it with them figuring they were going to come back and tell me it needed new cats or something.

But 2 hours later they called and told me that they had the problem diagnosed and corrected.

Turns out that the bank 1 upstream sensor needs to be programmed/calibrated. The tech did this with a machine that no private person would have and $45 later, I was on my way to get the car through Georgia emissions testing.

While 1273 can be a lot of things, I was surprised that in all the forums I'd visited that I had never run across the fact that this particular sensor needs to be specifically calibrated.

Who knew?

 

Weird, thanks for the heads up - do you have more details as to what exactly they did or what machine they used?

 

There is no calibration, only the mixture ratio self-learning which must be performed after replacing those sensors, once the engine is up to temp turn it off, unplug the MAF, turn it on and let it run for a minute, turn it off, plug back in the MAF, clear codes via OBD2, reset ECU either by OBD2 or pedal dance then let you're good to go and it will re-learn properly.

EDIT: There is a Nissan TSB somewhere about needing to re-learn after an O2 sensor replacement.