What it means
The system reports NOx exceedance associated with the EGR system. The code does not by itself identify a particular EGR component or failure.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The EGR system sends some exhaust gas back into the engine to reduce peak combustion temperatures and NOx formation. The control module detects that NOx emissions exceed the allowed level in an operating condition associated with EGR; this code alone does not pinpoint which EGR part or passage is responsible.
Common causes
Most likely first.
- EGR valve stuck closed
- Carbon clogged EGR passages
Symptoms
- Check engine light on
- Pinging or knocking under load
- Power loss and hesitation
- Possible rough idle
- Failed emissions inspection (NOx)
How to diagnose it
- Review freeze-frame data and NOx-related live data to see when the exceedance occurred and whether it coincided with load or temperature changes.
- Check for other emissions and EGR codes, since they may identify a valve, flow, or sensor issue contributing to this NOx result.
- Inspect the EGR valve connector, wiring, and accessible passages for damage, loose connections, or carbon blockage.
- Use a scan tool to command the EGR valve through its range, if supported, and compare commanded operation with its position or flow response.
- Check EGR passages for restriction and verify valve movement and NOx sensor readings using the vehicle's service information.
Common fixes
- Repair loose or damaged EGR wiring or connectors.
- Clean carbon from restricted EGR passages.
- Replace an EGR valve that is stuck or fails its movement test.
- Repair any separately confirmed NOx sensor or emissions-system fault.
Can I keep driving?
Avoid heavy acceleration or towing if the engine pings, hesitates, or loses power, and arrange diagnosis soon because sustained high NOx can cause emissions-test failure or trigger an operating restriction.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.