P224B code meaning
NOx Sensor Heater Resistance (Bank 1 Sensor 2)
Powertrain system Generic code P22xx codes Check engine light
What P224B means
P224B is the heater resistance fault of the second NOx sensor on bank 1, mounted after the SCR catalyst. This sensor tells the control unit how much NOx is left after dosing, so its readings feed the catalyst efficiency monitor and the closed-loop dosing correction. If the heater's resistance leaves its expected band, the element may be running too cold or too hot. No maker documents P224B publicly. GM's 2025 tables for the 3.0 L LZ0 Duramax check the post-catalyst sensor heater against a 3 % resistance window as well, but file it under P22A7, the sensor 2 heater sense performance code, Type B. Hella describes the integrated heater as the part that keeps the sensor at operating temperature regardless of exhaust conditions. P224A is the upstream counterpart.
P224B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 1.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P224B
- Check engine light
- SCR efficiency monitor delayed or failing
Common causes of P224B
- Most likelyHeating element of the downstream NOx sensor aged or damaged
- PossibleCorrosion in the sensor connector exposed to road spray
- Less likelyElement cracked by water droplets hitting the hot sensor
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Nox sensorNox sensor heater
What each part of P224B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 2 | Area: fuel and air metering (injector circuit). |
| 4B | The exact fault in that area. |
What to do next
- Note P224B 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 P224B
What does P224B mean?
P224B means "NOx Sensor Heater Resistance (Bank 1 Sensor 2)". P224B is the heater resistance fault of the second NOx sensor on bank 1, mounted after the SCR catalyst. It is a generic code, so it means the same on every make.
Is it safe to drive with P224B?
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 P224B fail an emissions test?
Yes, it can. P224B 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 P224B to fix?
Difficulty: medium. A typical repair takes 0.5 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P224B clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.