Powertrain, generic (extended)

P237A O2 Sensor Exhaust Sample Error (Bank 1 Sensor 2)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P237A says the rear oxygen sensor of bank 1 is not getting, or not reporting, a representative sample of exhaust: its reading does not fit the gas that should be flowing past it after the catalyst, typically because outside air enters through a leak or the sensing element is no longer exposed properly. No manufacturer documents P237A publicly. Volkswagen describes the front-sensor counterpart P2414 for the 2014 Golf with signal windows of 3.10 to 4.81 V and 2.5 to 3.2 V, which gives an idea of how such a plausibility check is built. CARB requires rear sensors to be monitored for faults that would spoil their use in catalyst and fuel control monitoring. P2414/P2415 cover sensor 1; code lists repeat this title under P23A0. Drivability is normally unaffected, but catalyst diagnosis becomes unreliable.

Likely causes

Leak at a flange, joint or cracked pipe ahead of the bank 1 rear sensor drawing in air
Rear sensor element damaged, coated or loose in its boss
Contaminated or blocked reference air path of the sensor (wiring or connector)

Symptoms

  • Check engine light on
  • Catalyst monitor not completing or reporting implausible results
  • Possible ticking exhaust noise from a leak

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 b1s2exhaust after catalyst b1

Related codes

P237BP23A0P2414P0136P232F

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