Powertrain, generic (extended)

P237B O2 Sensor Exhaust Sample Error (Bank 2 Sensor 2)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P237B is the bank 2 version of the sample check on the post-catalyst oxygen sensor and therefore only appears on engines with two exhaust banks, mostly V6 and V8 units with a separate downstream sensor on each side. The ECM decides that what the sensor reports cannot be genuine exhaust from that bank, for example because a leak at the second-bank pipe lets air in or the probe is mounted badly. No manufacturer documents P237B publicly; a published example of the method exists only for the front sensor, Volkswagen's P2414 on the 2014 Golf. CARB demands monitoring of rear sensors because the catalyst check relies on them. Related codes are P237A for bank 1 and P2415 for the bank 2 front sensor; code lists use this title again for P23A1. Inspecting the bank 2 exhaust for leaks comes first.

Likely causes

Air leak in the bank 2 exhaust between catalyst and rear sensor
Bank 2 rear sensor damaged, poisoned or not seated correctly
Rear sensors of bank 1 and bank 2 swapped at the connectors after a repair

Symptoms

  • Check engine light on
  • Bank 2 catalyst monitor incomplete or failing
  • Engine runs as usual

Repair estimate

DifficultyMediumDIY possible
Parts and labour€20–350
Time0.5–2 h

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

Parts involved

oxygen sensor b2s2exhaust after catalyst b2

Related codes

P237AP23A1P2415P0156P2379

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