P23B1 code meaning
NOx Sensor Heater Control Circuit/Open (Bank 1 Sensor 3)
Powertrain system Generic code P23xx codes Check engine light
What P23B1 means
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.
P23B1 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 P23B1
- Check engine light after one trip
- Sensor 3 never reports operating temperature
- SCR warning on the display
Common causes of P23B1
- Most likelyHeater element in the sensor 3 probe burnt through
- PossibleBroken heater conductor between probe and sensor module
- Less likelyProbe connector not fully engaged after a repair
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 P23B1 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. |
| B1 | The exact fault in that area. |
What to do next
- Note P23B1 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 P23B1
What does P23B1 mean?
P23B1 means "NOx Sensor Heater Control Circuit/Open (Bank 1 Sensor 3)". A NOx sensor only measures once its built-in heater has brought the ceramic element up to temperature. It is a generic code, so it means the same on every make.
Is it safe to drive with P23B1?
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 P23B1 fail an emissions test?
Yes, it can. P23B1 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 P23B1 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 P23B1 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.