Powertrain, generic (extended)

P225D NOx Sensor Performance - Signal Biased/Stuck Low (Bank 1 Sensor 1)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P225D is the opposite case to P225C: the upstream NOx sensor of bank 1 reads too little NOx or refuses to rise when the engine should be producing it. Volvo and Mack list P225D among NOx codes where the sensor is very unlikely to be at fault, because the probe is simply measuring fresh air; their guide says not to replace it. FCA uses P225D on the 3.0 EcoDiesel, from 2014 Ram 1500 and Grand Cherokee flash bulletins to 2020 Ram 1500 updates, and its 2021 case file for Wrangler, Gladiator and Ram 1500 reports mostly fault-free returned sensors; it names charge air or EGR leaks, fuel contamination that soots up the sensor ports and skewed MAF or coolant inputs. A low-reading sensor hides real NOx, so SCR control and the catalyst monitor lose accuracy.

Likely causes

Charge air, intake or exhaust leak that lets the sensor see diluted gas
Sensor ports clogged with soot, for example after fuel contamination
Low-pressure EGR valve partly stuck open
Outdated engine control software that a published flash corrects

Symptoms

  • MIL on
  • Code persists after a new NOx sensor
  • Possible related intake, EGR or MAF codes

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–900
Time0.5–3 h

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

Parts involved

nox sensor

Related codes

P225CP225FP2201P2202P20EE

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.