P2A00 - A/F Sensor Circuit Range/Performance (bank 1 sensor 1)

Originally Posted by Jordo!

Check for vac leaks by spraying carb cleaner all along the intake tract, after the MAF, up to and around the IM gasket -- no change in idle means no leaks. You'll have to get it on a lift to check around the O2 bung on the header.

If no evidence of any vac leaks then do some datalogging with cipher.

Confirm similar voltage on bank and 2 MAF's and also log AFR and AF voltage readings on both primary O2's (note that weirdly cipher sometimes labels both as "bank 1"), fuel trims, and heater sensor correction %.

Wildly different voltage between the banks points to one sensor or the wires (if you have extenders) or both being bad -- based on that code, Bank 1 should be skewing way lean compared to Bank 2. You will also see massive fuel correction when that happens as the ECU tries to catch itself and keep on target.

Also note heater correction %: Low correction (say up to 30%) means normal warm up; high correction (close to 100%) means bad sensor, bad wires or both (usually bad sensor).

I just had similar problem, same code (same bank, in fact) eventually started getting constant low heater code for that bank.

New sensor already ordered.

If you find no evidence of different voltages, corrections etc, then its random and meaningless... however, I'm betting on a bad Bank 1 upstream O2.