OBD-II · Engine and powertrain (P)
P2209
NOx sensor heater sense circuit range/performance bank 1 sensor 1
What it means
The feedback circuit used to monitor the NOx sensor 1 heater is outside its expected range or behaves implausibly; actual heater temperature may or may not be incorrect. NOx sensor 1 is usually the one before the AdBlue catalyst. NOx sensors measure exhaust nitrogen oxides for emissions control and monitoring, including SCR or NOx-storage systems. The probe and its control module normally form a matched assembly. On vehicles with SCR, a confirmed unresolved fault may trigger reduced performance or a no-restart countdown; follow the displayed warning and the vehicle handbook.
Symptoms
- engine warning light and/or AdBlue/emissions warning
- possibly a no-start countdown
- usually no change in how the car drives
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | ageing NOx sensor heater |
| 02 | low supply voltage |
| 03 | exhaust leak or unusual cooling near the sensor |
| 04 | wiring resistance |
What to check, step by step
- 01Read all NOx/SCR codes and NOx sensor live data (sensor ready status and values).
- 02Check the sensor module's fuse, power supply and ground.
- 03Inspect the connector and wiring along the exhaust for heat damage and water ingress.
- 04Check for exhaust leaks near the sensor.
- 05Replace the correctly identified probe/module assembly only if the diagnostic tests confirm an internal sensor fault; use the specified compatible part.
- 06After repair, perform any required sensor initialization or adaptation, clear repairable faults, and complete the OEM validation drive cycle.