Powertrain, generic (extended)

P23BF NOx Sensor Performance - Slow Response Low to High (Bank 1 Sensor 3)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P23BF concerns how quickly NOx sensor 3 on bank 1 follows a rise in NOx. The control module waits for an increasing transient and times the climb of the sensor signal against what a model predicts. No manufacturer publishes P23BF. GM's 2025 table demonstrates the method on the front sensor under P22F9: timing runs from 30 ppm up to 220 ppm, and the sensor fails when it trails by over 2 s or by more than a tenth of the model's time. For a probe behind two SCR catalysts this is harder, since little NOx is left to reach it. A Continental smart sensor is specified with a 33-66 % response time of 1300 ms when fresh and 1650 ms when aged. CARB counts response rate among NOx sensor performance faults. P22F9 and P22FC are sensors 1 and 2; P23C0 is the falling edge.

Likely causes

Soot, oil ash or urea residue blocking the gas inlet of the sensor
Measuring cells aged beyond their response specification
Element running too cold because the heater is weak

Symptoms

  • Check engine light on
  • Sensor 3 signal trails the front sensor during acceleration
  • No change in how the engine runs

Repair estimate

DifficultyMediumDIY possible
Parts and labour€150–900
Time0.5–2 h

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

Parts involved

nox sensor b1s3

Related codes

P23C0P23C2P22F9P22FC

References: law.cornell.edu, gsi.ext.gm.com, ni.com.