Dear Laozong,

May this find you well. 2-3-1 could be the result of:
(a) failing fuel pump(s) and/or partly plugged fuel filter
(b) failing fuel regulator (at the front of the fuel rail, above intake manifold)
(c) failing fuel system relay (on main relay block, behind front center console)
(d) failing radio interference suppression relay (fuel injectors' relay, in the engine bay, against the right inner fender wall, forward of the ABS unit [passenger side, USA/Canada models]).

I'd start by replacing the relays, with known good units (from a salvage yard, or the parts department). If you do not know, when the fuel filter was last changed, that, too, should be done. The fuel regulator can be checked, by removing the small hose (if my memory serves me correctly: see the FAQs, under FEATURES, above). If there's liquid fuel in that hose, the regulator should be replaced.

As to the oxygen sensor:
(a) it or its wiring, could have been damaged by road debris (unlikely but possible)
(b) even though new, it could still have failed
(c) its connector could have come loose (unlikely, but possible).

Please post back, with your findings.

Yours faithfully,

spook