P23B6 code meaning
NOx Sensor Supply Voltage Circuit (Bank 1 Sensor 3)
Powertrain system Generic code P23xx codes Check engine light
What P23B6 means
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.
P23B6 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P23B6
- 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
Common causes of P23B6
- Most 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
- Less likelyWeak battery or charging fault pulling the sensor supply down
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Nox sensor b1s3
What each part of P23B6 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 3 | Area: ignition system or misfire. |
| B6 | The exact fault in that area. |
What to do next
- Note P23B6 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P23B6
What does P23B6 mean?
P23B6 means "NOx Sensor Supply Voltage Circuit (Bank 1 Sensor 3)". P23B6 concerns the power feed of the third NOx sensor on bank 1, the smart probe behind the second SCR catalyst. It is a generic code, so it means the same on every make.
Is it safe to drive with P23B6?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P23B6 fail an emissions test?
Yes, it can. P23B6 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P23B6 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P23B6 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.