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.
Medium severity. Can I keep driving?You can usually keep driving in the short term, but get it repaired soon: on many diesels, the warning eventually limits starting or engine power.
Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.
Symptoms
- Check engine light
- SCR efficiency monitor delayed or failing
Most likely causes
- Heating element of the downstream NOx sensor aged or damaged
- Corrosion in the sensor connector exposed to road spray
- Element cracked by water droplets hitting the hot sensor
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P224B means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 2: Fuel injection
- 4B: Specific fault in that system
Frequently asked questions
Can I keep driving with code P224B?
You can usually keep driving in the short term, but get it repaired soon: on many diesels, the warning eventually limits starting or engine power.
What causes code P224B?
The most common causes are: heating element of the downstream NOx sensor aged or damaged; corrosion in the sensor connector exposed to road spray; element cracked by water droplets hitting the hot sensor.
Related codes
- P224ANOx Sensor Heater Resistance (Bank 1 Sensor 1)
- P22A7NOx Sensor Heater Sense Circuit Range/Performance (Bank 1 Sensor 2)
- P220FNOx Sensor Heater Control Circuit Range/Performance (Bank 1 Sensor 2)
- P0054HO2S Heater Resistance Bank 1 Sensor 2
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.