P23A1 O2 Sensor Exhaust Sample Error (Bank 2 Sensor 2) - Duplicate Listing of P237B

P23A1 is listed with the same title as P237B: the bank 2 oxygen sensor behind the catalyst reports something that cannot be genuine exhaust from that bank. Only engines with two exhaust banks and a downstream sensor on each side could produce it. No published OBD summary or bulletin assigns P23A1, and no source gives it its own meaning; it is thus a duplicate listing of P237B, itself without public manufacturer use. A comparable plausibility check is documented only for a front sensor, Volkswagen's P2414 on the 2014 Golf. Should the code appear, the manufacturer's definition takes precedence; practical checks cover air leaks on the bank 2 pipe, sensor position and wiring. CARB demands that rear sensors are monitored because catalyst diagnosis depends on them.

Likely causes

Symptoms

• MIL on, engine runs normally
• Readiness for catalyst monitor stays open

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, static.nhtsa.gov, en.wikipedia.org.