Powertrain, generic (extended)

P23B2 NOx Sensor Heater Control Circuit Low (Bank 1 Sensor 3)

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23B2 points to the heater control line of bank 1's NOx sensor 3 being pulled to ground. GM's 2025 diesel table 25OBDG04B checks that pin on the sensor downstream of the second catalyst for a short to ground and, unlike the open-circuit test, waits until the dew point has been reached, so that the heater is actually allowed to run; 80 failed out of 160 samples set the code. GM rates it Type B, two trips before the MIL lights. The bulletin for the 3.0L LM2 diesel, 21-NA-149 (model years 2021–2022), lists the code too and traces many faults to chafed engine harnesses. CARB demands detection of heater circuit shorts that contradict what the heater was told to do. The heater can then no longer be regulated; P23B3 is the short to power.

Likely causes

Heater control wire chafed against ground
Internal short in the heater of sensor 3
Water bridging the heater pins in the connector

Symptoms

  • Check engine light after two trips
  • Sensor 3 slow or unable to become ready

Repair estimate

DifficultyMediumDIY possible
Parts and labour€100–1,000
Time0.5–2.5 h

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

Parts involved

nox sensor b1s3 heater

Related codes

P23B1P23B3P23B7P2206P22A4

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