Powertrain, generic (extended)

P224B NOx Sensor Heater Resistance (Bank 1 Sensor 2)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

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

Symptoms

  • Check engine light
  • SCR efficiency monitor delayed or failing

Repair estimate

DifficultyMediumDIY possible
Parts and labour€250–900
Time0.5–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

nox sensornox sensor heater

Related codes

P224AP22A7P220FP0054

References: law.cornell.edu, gsi.ext.gm.com, hella.com.