Powertrain, generic (extended)

P229F NOx Sensor Circuit Range/Performance (Bank 1 Sensor 2)

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P229F says the rear NOx sensor on bank 1 is electrically sound but its reading fails a plausibility test. Methods vary. GM's 6.6L LML waits for a burst of engine-out NOx and faults the sensor if its own value moves by less than 3 ppm (Type B); the 3.0L LZ0 watches the stability of the internal pump currents, failing above 0.5 percent unstable time. Ford checks offsets of roughly 30 ppm low or 50 ppm high and a missing rise on tip-in; VW's 2014 Touareg TDI checks offset, self-diagnosis results and oxygen plausibility. Volvo and Mack explain that P229F-64 can set when a fresh SCR leaves almost no NOx, so a single event is no proof of a bad sensor. Hino wants DEF quality and dosing checked first, and Ford warns that EGR cleaning fluids poison NOx sensors.

Likely causes

Outlet NOx element drifted, slow or poisoned (e.g. sodium from cleaning fluids)

Poor DEF quality or faulty dosing that distorts downstream NOx

Harness or connector fault at the outlet sensor (Volvo/Mack P229F-64)

Engine or dosing software needing an update (several FCA, Hino, Mazda notices)

Symptoms

Malfunction indicator lamp on
Often stored together with SCR efficiency code P20EE
Downstream NOx value implausible compared with the upstream sensor

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€0–1,100

Time0.5–3 h

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

Parts involved

nox sensorscr catalyst

References: gsi.ext.gm.com, gsi.ext.gm.com, fordservicecontent.com, static.nhtsa.gov.