P2203 — NOx Sensor Circuit High Input (Bank 1 Sensor 1)
Severity: medium
Drive with care, to a shop
What P2203 means
The engine control module monitors the nitrogen oxide (NOx) sensor in the exhaust ahead of the SCR catalyst. This signal helps set how much urea (DEF/AdBlue) gets injected. P2203 sets when the circuit voltage is too high or the circuit is open.
Symptoms
- Check Engine light on
- SCR or AdBlue/DEF warning
- Emissions test failure
- Possible power or torque limitation
- Start countdown on some vehicles
Possible causes
- Open circuit in the NOx sensor wiring
- Failed NOx sensor
- Broken wire near the DPF/SCR assembly
- Wiring shorted to positive voltage
- Corroded or damaged sensor connector or sensor control module
How to diagnose
- Read codes and freeze frame data and look for other SCR-related codes
- View NOx sensor readings and dosing system status on a scan tool
- Check the DEF level and quality
- Inspect the harness and connector for damage, heat marks and corrosion
- Test power, ground and signal circuits with a multimeter, checking for opens and shorts to positive
- Inspect the dosing valve, lines and heater operation
- Check for technical service bulletins and ECM software updates
Common fixes
- Repair or replace damaged wiring and connectors
- Replace the NOx sensor
- Replace the sensor control module if separate and faulty
- Update the ECM software per manufacturer bulletin
- Clear the code and confirm SCR operation on a test drive
Questions and answers
Can I drive with P2203?
Briefly, usually yes, but do not put it off. Some vehicles will limit power or prevent a restart after a countdown.
What most often causes P2203?
Most often it is the NOx sensor itself or damaged wiring and connectors near the SCR catalyst. Check the harness first, then replace the sensor if needed.
This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.