Powertrain, generic (extended)

P23B3 NOx Sensor Heater Control Circuit High (Bank 1 Sensor 3)

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

If, on NOx sensor 3 of bank 1, the heater control pin sits at supply voltage when the electronics expect it to switch, P23B3 is stored. GM's 2025 diesel table 25OBDG04B describes it, for the sensor behind the second catalyst, as a battery short at the heater drive pin, evaluated every 25 ms with sensor supply above 9.9 V and dew point reached, and failing at 80 of 160 samples; Type B with the MIL on the second trip. GM also lists P23B3 in bulletin 21-NA-149 for 3.0L LM2 Duramax light trucks of 2021–2022. CARB requires the OBD system to catch heater circuit states that contradict the command, naming a short to 12 V as the example. As electronics and heater form one unit, the complete sensor is usually replaced once the harness is ruled out. P23B2 is the ground short.

Likely causes

Heater control wire shorted to a supply line
Heater driver inside the sensor 3 electronics failed
Heat-damaged connector with pins touching

Symptoms

  • Check engine light after two trips
  • Sensor 3 heater status shows an error in live data
  • SCR warning

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

P23B1P23B2P23B7P2207P22A5

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