P224BNOx Sensor Heater Resistance (Bank 1 Sensor 2)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Check engine light
- SCR efficiency monitor delayed or failing
- Likely causes
- LikelyHeating element of the downstream NOx sensor aged or damaged
- PossibleCorrosion in the sensor connector exposed to road spray
- RareElement cracked by water droplets hitting the hot sensor
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €250 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.