Powertrain, generic (extended)

P225F NOx Sensor Performance - Signal Biased/Stuck Low (Bank 1 Sensor 2)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P225F is set when the downstream NOx sensor of bank 1 reports less NOx than expected or does not move away from a low value. A sensor behind the SCR catalyst that reads too low makes the catalyst look better than it is, so the efficiency monitor can no longer be trusted. The only public manufacturer source is the Volvo and Mack NOx sensor replacement guide for US10 and newer trucks: it lists P225F next to P225D among codes whose description mentions the NOx sensor although the sensor is rarely the cause, notes that the probe is reading fresh air, and tells technicians not to replace it. Leaks in the exhaust ahead of the sensor and harness faults are the more likely culprits. P225D is the upstream case; P225E the high-reading counterpart.

Likely causes

Exhaust leak upstream of the downstream sensor drawing in outside air
Chafed or corroded wiring between sensor module and probe
Downstream NOx sensor with reduced sensitivity

Symptoms

  • MIL on
  • SCR efficiency cannot be confirmed, readiness may stay open

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–900
Time0.5–3 h

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

Parts involved

nox sensor

Related codes

P225DP225EP229EP20EE

References: static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.