Emissions Control: SCR System Efficiency Below Threshold
The SCR system is not working as efficiently as it should be.
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 SCR system uses diesel exhaust fluid to reduce harmful emissions. If there's an issue, it means the system isn't converting enough of the harmful gases, which could lead to increased pollution.
What the computer is actually seeing
The Engine Control Module (ECM) detects that the amount of NOx (Nitrogen Oxides) being converted by the SCR system is below an acceptable level, meaning less than 90% efficiency during a specified cycle.
What a healthy reading looks like
The SCR efficiency should be above 90% under normal conditions; otherwise, the system triggers this fault.
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 fluid level; it should be above the minimum threshold. If it's low, refill and clear codes.
- 22. Inspect DEF quality; ensure it meets ISO 22241 standards. If contaminated, drain and refill with fresh DEF.
- 33. Check the wiring and connectors to the SCR system for any damage or corrosion. Repair as necessary.
- 44. Test the SCR catalyst for proper function; consider a backpressure test or consult the manufacturer’s specifications.
- 55. Measure the exhaust temperature pre and post-SCR. If the readings are not within expected values, the SCR may be faulty.
Common causes
- Low DEF fluid level
- Contaminated DEF (wrong fluid mixed)
- Faulty SCR catalyst
- Issues with the exhaust temperature sensor
- Electrical issues in SCR wiring or connectors
Typical repair cost
$$-$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
Yes, but emissions will be higher and it may lead to further issues if not addressed.
Will this code come back if I reset it?
If the underlying issue isn't fixed, the code will likely return.
Why is it paired with other codes?
Because multiple sensors can indicate the overall health of the SCR system, often showing issues together.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →