SCR NOx Reductant Injection System Performance
This code indicates an issue with the SCR system's NOx reductant injection performance.
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)
The computer is sensing that the system designed to inject urea (DEF) into the exhaust stream is not working correctly, which is needed to reduce harmful NOx emissions.
What the computer is actually seeing
The Engine Control Module (ECM) monitors the flow and quality of the urea being injected. It expects precise injection rates to match the required levels for effective NOx reduction.
What a healthy reading looks like
Expected urea dosing rates usually fall within 0.2 to 1.5 liters per hour depending on engine load and operating conditions; urea quality needs to meet standard (APU) specifications.
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.
- 11. Check the DEF level in the tank; it should be between the minimum and maximum marks. If low, refill and see if the code returns.
- 22. Inspect the DEF injector and lines for any clogs or damage. Ensure that the injector is not blocked. Test or replace if necessary.
- 33. Measure the electrical connections at the injector for any shorts or opens. Use a multimeter to ensure continuity and proper resistance (1-10 ohms).
- 44. Test the NOx sensor operation. Compare actual readings to expected values. If readings are outside normal parameters, replace the sensor.
- 55. Clear the codes and take the vehicle on a test drive to check if the code reappears.
Common causes
- Clogged or faulty DEF injector
- Low DEF tank level
- Blocked DEF lines
- Contaminated DEF fluid
- Faulty NOx sensor or wiring
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not advisable to drive long distances with this code. It may cause increased emissions and potential legal issues.
Will this code come back after repairs?
If no underlying issues exist and repairs are done correctly, the code should not return.
Why does this code sometimes pair with other codes?
It may indicate that multiple issues exist in the SCR system, often related to the quality of the DEF fluid or NOx sensor performance.
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