P23B3 code meaning
NOx Sensor Heater Control Circuit High (Bank 1 Sensor 3)
Powertrain system Generic code P23xx codes Check engine light
What P23B3 means
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.
P23B3 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P23B3
- Check engine light after two trips
- Sensor 3 heater status shows an error in live data
- SCR warning
Common causes of P23B3
- Most likelyHeater control wire shorted to a supply line
- PossibleHeater driver inside the sensor 3 electronics failed
- Less likelyHeat-damaged connector with pins touching
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Nox sensor b1s3 heater
What each part of P23B3 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. |
| B3 | The exact fault in that area. |
What to do next
- Note P23B3 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 P23B3
What does P23B3 mean?
P23B3 means "NOx Sensor Heater Control Circuit High (Bank 1 Sensor 3)". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P23B3?
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 P23B3 fail an emissions test?
Yes, it can. P23B3 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 P23B3 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P23B3 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.