Powertrain, generic (extended)

P23B6 NOx Sensor Supply Voltage Circuit (Bank 1 Sensor 3)

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P23B6 concerns the power feed of the third NOx sensor on bank 1, the smart probe behind the second SCR catalyst. Its built-in control unit needs a stable supply, and when the voltage it reports leaves the allowed range the engine module stores this code. GM's 2025 diesel table 25OBDG04B fails it below 9.90 V while the engine runs, the powertrain relay delivers more than 11 V and the dew point has been passed; it needs 125 bad readings among 250 taken every 25 ms and is rated Type B (two-trip MIL). In bulletin 21-NA-149 GM counts P23B6 among the codes produced by a chafed engine harness with blown fuses on 2021-2022 trucks with the 3.0L LM2. P220A and P220B are the same check on sensors 1 and 2; without proper supply the sensor sends no NOx values.

Likely causes

Blown fuse in the NOx sensor supply after a short elsewhere in the harness
Supply or ground wire chafed through on the engine or frame (GM 3.0L LM2)
Corroded or loose pins in the sensor 3 connector under the vehicle
Weak battery or charging fault pulling the sensor supply down

Symptoms

  • Check engine light after two trips
  • Sensor 3 shows no NOx value in live data
  • Further NOx sensor or communication codes stored at the same time

Repair estimate

DifficultyMediumDIY possible
Parts and labour€20–900
Time0.5–3 h

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

Parts involved

nox sensor b1s3

Related codes

P23ABP23ACP220AP220B

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