Powertrain, generic (extended)

P225C NOx Sensor Performance - Signal Biased/Stuck High (Bank 1 Sensor 1)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P225C says the upstream NOx sensor of bank 1 reports more NOx than is plausible. Volvo describes its test on US17+OBD19 trucks: during engine motoring with zero fuel the engine makes no NOx, so the inlet sensor must fall below 50 ppm within about 10 s; each failure lights the MIL, which needs three clean drive cycles to go out. Volvo admitted false settings and told dealers not to replace the sensor. Mack and Volvo (KC-107) demand a NOx conversion test first; inlet and outlet should agree within 40 ppm before shutdown. Isuzu cured P225C on 2021 F-Series 5.2L trucks with a DCU update. FCA found most returned sensors from 3.0 EcoDiesel Ram and Jeep models fault-free and points to intake or EGR leaks, soot-clogged sensor ports and skewed MAF or coolant readings.

Likely causes

Engine or DEF control unit software that flags the sensor too eagerly
Leak in the charge air path or an EGR valve stuck partly open
Air mass or coolant temperature signal that skews the NOx model
Upstream NOx sensor with a genuine positive offset

Symptoms

  • MIL on, often without any noticeable driving fault
  • Code returns after the NOx sensor has been replaced
  • Higher DEF consumption or SCR efficiency codes in some cases

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

P225DP225EP2201P221AP20EE

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