P229F — NOx Sensor Circuit (Downstream)
NOx sensor circuit fault (downstream / bank 1 sensor 2).
P229F indicates an electrical or signal fault from the downstream NOx sensor — the one mounted after the SCR catalyst. It is one of the most frequently logged Euro 6 codes on Mercedes Sprinter, BMW, Audi and Land Rover diesels.
P229F symptoms
- AdBlue / Check Engine light
- 'AdBlue — no engine start' countdown
- Intermittent limp mode
- Sister code P20EE often appears alongside
Common causes of P229F
Sensor element failure
Thermal cycling and exhaust contamination degrade the heated zirconia element.
Wiring or connector damage
Heat-damaged loom or corroded connector at the sensor end.
Control module fault (rare)
Some vehicles use a sensor with an integrated module that can fail independently.
Exhaust leak near sensor
Air ingress confuses the signal.
Vehicles affected by P229F
- • Mercedes-Benz Sprinter, Vito, C-Class, E-Class (OM651 / OM642)
- • BMW X5, 5 Series, 3 Series (N57 / B47)
- • Audi A6, A4, Q7 (3.0 TDI)
- • Land Rover Discovery, Range Rover (TDV6 / Ingenium)
- • Ford Transit (2.0 EcoBlue)
- • VW Crafter, Touareg (2.0 / 3.0 TDI)
P229F diagnostic process
- Read live mV / ppm output from upstream and downstream NOx sensors
- Check sensor heater circuit resistance
- Inspect wiring loom and connector
- Confirm fault is sensor-side, not exhaust leak or wiring
Common P229F repairs
- Replace downstream NOx sensor with OE-quality coded part
- Code new sensor to vehicle (Xentry / VCDS / IDS)
- Repair damaged wiring or connector
- Reset SCR adaptations and clear stored codes
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