Powertrain, generic (extended)

P23A0 O2 Sensor Exhaust Sample Error (Bank 1 Sensor 2) - Duplicate Listing of P237A

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P23A0 repeats, word for word, the title of P237A in the usual code lists: the rear oxygen sensor of bank 1 does not see, or does not report, a representative sample of post-catalyst exhaust. No manufacturer uses P23A0 in any published OBD table or service bulletin, and no source defines it differently, so it is a duplicate listing of P237A. Even P237A has no public manufacturer application; the method is known only from the front sensor, where Volkswagen documents P2414 for the 2014 Golf with fixed signal windows. If a tool reports P23A0, check the maker's own code text first, then inspect the exhaust ahead of sensor 2 for air leaks and the probe's mounting. CARB requires monitoring of rear sensors used for catalyst checks.

Likely causes

Scan tool code table using the duplicate number

Air leak in the exhaust ahead of the rear sensor on bank 1

Sensor mounted poorly or element contaminated

Symptoms

MIL on, no drivability change
Catalyst diagnosis unreliable or incomplete

Repair estimate

DifficultyMediumDIY possible

Parts and labour€0–350

Time0.3–2 h

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

Parts involved

oxygen sensor b1s2

Related codes

P237A P23A1 P2414

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