P23B6NOx Sensor Supply Voltage Circuit (Bank 1 Sensor 3)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- 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.
- What you may notice
- 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
- Likely causes
- LikelyBlown fuse in the NOx sensor supply after a short elsewhere in the harness
- PossibleSupply or ground wire chafed through on the engine or frame (GM 3.0L LM2)
- PossibleCorroded or loose pins in the sensor 3 connector under the vehicle
- RareWeak battery or charging fault pulling the sensor supply down
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €20 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.