NOx Sensor Circuit High Input Bank 1 Sensor 1
The DURAMAX-P2203 (Duramax) diesel fault code means: NOx Sensor Circuit High Input Bank 1 Sensor 1. This is a serious severity code.
- Keep driving?
- Yes, with caution
- DIY difficulty
- advanced
- Estimated cost
- $300-$500 NOx sensor, $200 DEF injector, $2,500-$4,500 full SCR replacement
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View pilot availability →What Are the Symptoms of DURAMAX-P2203?
- Check Engine Light
- 'Service Emissions System' or 'Service DEF System' message
- Countdown to speed limit reduction (5 mph eventually) if uncorrected
- Extra DEF consumption
- DPF regen occurring more frequently
What Causes DURAMAX-P2203? (Most Likely First)
- Upstream NOx sensor shorted high / open Very Likely
- Contaminated DEF fluid (use ONLY API-certified DEF) Likely
- DEF injector clogged with crystallized urea Possible
- NOx sensor end-of-life (typical 100-150K miles) Possible
- Wiring or connector fault at sensor Possible
Can I Still Drive with DURAMAX-P2203?
Yes, with caution. DURAMAX-P2203 is rated serious severity. Keep trips short and get it diagnosed soon rather than waiting for symptoms to worsen.
Frequently Asked Questions
What is P2203 on a Duramax?
Duramax code P2203 (NOx Sensor Circuit High Input Bank 1 Sensor 1) is a serious-severity diagnostic trouble code triggered by the engine control module when it detects a problem in the associated system. ALWAYS use API-certified DEF from a sealed container. Contaminated or wrong DEF is the #1 cause of SCR system failure.
Is a Duramax P2203 safe to drive?
Short-term yes, but the PCM enters a countdown that reduces top speed to 5 mph if the fault isn't cleared. Repair before hitting 0 miles remaining.
How much does it cost to fix P2203 on a Duramax?
NOx sensor $300-$500 installed. DEF injector $200-$400. SCR catalyst $2,500-$4,500.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose DURAMAX-P2203?
Scan for all SCR codes together — a single NOx sensor failure often cascades into multiple DTCs
Verify DEF quality — use a refractometer or DEF test strips (should be 32.5% urea ± 0.5%)
Inspect the DEF injector for crystallized urea deposits; clean or replace
If both upstream and downstream NOx sensors are reading the same value at idle, one may be failed
Use Tech 2 / GDS2 to run SCR performance tests after repair to clear countdown
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines P2203 as a generic OBD-II code)
P2203 on Other Platforms
The same code ID appears across other engines, vehicles, and equipment. Diagnostic flow varies by platform — see the matching breakdown:
Which Vehicles Commonly Get DURAMAX-P2203?
- 2011-2016 Chevy Silverado 2500/3500 HD 6.6L Duramax LML
- 2011-2016 GMC Sierra 2500/3500 HD 6.6L Duramax LML
- 2017+ Chevy Silverado 2500/3500 HD 6.6L Duramax L5P
- 2017+ GMC Sierra 2500/3500 HD 6.6L Duramax L5P
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