Excessive SCR NOx Emissions Detected
The system detected NOx emissions above the allowable limit.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
Your diesel vehicle is producing too much nitrogen oxide (NOx), which is not good for the environment and can lead to increased emissions fines.
What the computer is actually seeing
The engine control module (ECM) watches the NOx sensor signals and compares them against baseline parameters. If NOx levels exceed the range of about 0-1000 ppm for a specific duration or reach over 1500 ppm momentarily, it flags this code.
What a healthy reading looks like
Normal NOx levels should be fluctuating between 0-1000 ppm during operation.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check the vehicle's DEF level; ensure it is Above 1/4 full. If low, refill and rerun the system.
- 2Inspect the wiring and connector for the NOx sensor for damage or corrosion, repair if found.
- 3Measure NOx levels directly using a scan tool; compare with expected values. If readings are above 1000 ppm, continue diagnostics.
- 4Perform a visual inspection for any exhaust leaks around the SCR and NOx sensor area. Fix any leaks found.
- 5If all checks are good, test the NOx sensor with a multimeter. Compare the output voltages to manufacturer specifications.
Common causes
- Faulty NOx sensor
- Faulty SCR system
- Exhaust leaks affecting readings
- Software issues in ECM or SCR control system
- Improper DEF fluid quality or concentration
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
Not recommended. High NOx emissions can lead to fines and potential damage to the emissions system.
Will this code come back after clearing?
It may return if the underlying issue isn't fixed.
Why does this code appear with other NOx codes?
They often indicate issues with the SCR system, so they can show up together if there's a common failure.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
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