P23B4 code meaning
NOx Sensor Heater Sense Circuit (Bank 1 Sensor 3)
Powertrain system Generic code P23xx codes Check engine light
What P23B4 means
Besides its drive line, the heater of a NOx sensor has a sense connection through which its resistance, and with it the element temperature, is measured. P23B4 reports a fault in that sense path for the third sensor on bank 1. GM's 2025 diesel table 25OBDG04B checks the HTemp pin of the post-second-catalyst sensor for an open circuit: 80 of 160 samples, Type A, MIL after one trip. A note in the table says that the Continental Gen 3.5 sensors debounce electrical faults internally for 1.5 s before reporting them, which lets the affected wire be pinpointed. Bulletin 21-NA-149 adds P23B4 to the harness-chafe list of LM2-powered 3.0L trucks from 2021–2022. Heater circuit monitoring is a CARB requirement. P23B5 is the plausibility check, P2208 and P22A6 the other sensors.
P23B4 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 P23B4
- Check engine light after one trip
- Sensor 3 temperature status invalid
Common causes of P23B4
- Most likelyHeater sense lead broken between probe and module
- PossibleBacked-out or corroded terminal at the probe connector
- PossibleInternal break in the sensor 3 probe
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 P23B4 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. |
| B4 | The exact fault in that area. |
What to do next
- Note P23B4 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 P23B4
What does P23B4 mean?
P23B4 means "NOx Sensor Heater Sense Circuit (Bank 1 Sensor 3)". Besides its drive line, the heater of a NOx sensor has a sense connection through which its resistance, and with it the element temperature, is measured. It is a generic code, so it means the same on every make.
Is it safe to drive with P23B4?
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 P23B4 fail an emissions test?
Yes, it can. P23B4 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 P23B4 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 P23B4 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.