Powertrain, generic (extended)

P23AE NOx Sensor Circuit Low (Bank 1 Sensor 3)

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23AE is set when the third NOx sensor on bank 1 reports a concentration below anything physically possible. GM's 25OBDG04B table for its 2025 diesels requires the raw NOx value of the sensor behind the second catalyst to fall under −90 ppm in 100 of 200 samples, taken every 25 ms once dew point is reached, supply exceeds 9.9 V and no CAN fault is present; it is rated Type B with the MIL after two trips. GM bulletin 21-NA-149 lists P23AE among the codes caused by chafed engine harnesses on 3.0L LM2 Duramax pickups and SUVs of 2021–2022 (Silverado and Sierra 1500, Tahoe, Suburban, Yukon, Escalade). CARB demands out-of-range checks on NOx sensors. P23AF is the high limit, P2202 and P22A0 are the low codes of sensors 1 and 2.

Likely causes

Engine harness chafed, disturbing the sensor 3 supply or signal
Sensor 3 with a negative offset from ageing or damage
Water in the sensor connector

Symptoms

  • Check engine light after two trips
  • Negative or zero NOx value for sensor 3 in live data
  • Other harness-related codes stored at the same time

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–900
Time0.5–3 h

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

Parts involved

nox sensor b1s3

Related codes

P23AFP23ADP23ACP2202P22A0

References: gsi.ext.gm.com, static.nhtsa.gov, law.cornell.edu.