P2203 — NOx Sensor Circuit High Input (Bank 1)
Moderate severityWhat it means
P2203 is stored when the engine control unit sees a fault involving the NOx (nitrogen oxide) sensor circuit on bank 1. The NOx sensor measures nitrogen-oxide emissions so the control unit can manage the catalyst or SCR system on modern (especially diesel) engines. A “high” reading means the signal is pinned near the top of its range — often an open circuit, a lost ground, or a short to voltage.
Common symptoms
- The live reading sits abnormally high or maxed out
- Reduced power or limp mode
- Increased emissions and DEF/AdBlue warnings
- Check engine light
Likely causes
- Open signal or ground wire
- Signal wire shorted to a voltage supply
- A faulty NOx sensor
- A wiring/connector fault, often from exhaust heat
What to check first
- Check for an open circuit or missing ground at the sensor connector
- Compare NOx sensor readings in live data
- Inspect the sensor and its heat-exposed wiring
Can you keep driving?
Often drops to reduced power to protect emissions hardware; diagnose soon on a modern diesel.
Frequently asked questions
What is the most common cause of P2203?
The most likely cause is: Open signal or ground wire. Several other faults can set P2203 as well, so confirm the real cause with live data and the checks above before replacing any parts.
Can I just clear P2203 and keep driving?
Clearing P2203 with an OBD2 scanner turns the warning light off, but if the underlying fault has not been repaired the code will usually come back within a few drive cycles. Fix the cause first, then clear the code to confirm the repair worked.
How serious is P2203?
P2203 is a moderate-severity code. The car is often still drivable, but have it diagnosed soon — the underlying problem can get worse and it may fail an emissions test.
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