Powertrain, generic (extended)

P23B1 NOx Sensor Heater Control Circuit/Open (Bank 1 Sensor 3)

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

A NOx sensor only measures once its built-in heater has brought the ceramic element up to temperature. P23B1 reports that the heater control side of the third sensor on bank 1 is open. GM's 2025 diesel calibration (table 25OBDG04B) looks for a missing load on the heater control pin of the post-second-catalyst sensor and fails after 80 of 160 samples at a 25 ms rate, with powertrain relay voltage above 11 V and the sensor bus relay switched on. GM rates it Type A, so the MIL comes on after a single trip. Bulletin 21-NA-149 includes P23B1 in its chafed-harness list for 2021–2022 3.0L LM2 trucks. CARB requires heater circuits to be checked for opens and shorts. P23B2 and P23B3 are shorts; P2205 and P22A3 cover sensors 1 and 2.

Likely causes

Heater element in the sensor 3 probe burnt through
Broken heater conductor between probe and sensor module
Probe connector not fully engaged after a repair

Symptoms

  • Check engine light after one trip
  • Sensor 3 never reports operating temperature
  • SCR warning on the display

Repair estimate

DifficultyMediumDIY possible
Parts and labour€150–1,000
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

P23B2P23B3P23B4P23B7P2205P22A3

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