SCR NOx Catalyst Efficiency Below Threshold
The YANMAR-P20EE (Yanmar) diesel fault code means: SCR NOx Catalyst Efficiency Below Threshold. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- advanced
- Estimated cost
- $300-$3,500
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Common Symptoms
- 3-stage derate countdown, DEF lamp
Probable Causes (Ranked by Likelihood)
- Contaminated DEF fluid Likely
- Failed downstream NOx sensor Likely
- Aged SCR catalyst Possible
Step-by-Step Diagnostic Procedure
Test DEF with refractometer (32.5%).
Scan both NOx sensors under load.
Check SCR dosing rate.
Frequently Asked Questions
What is Yanmar code P20EE?
Yanmar P20EE: SCR NOx Catalyst Efficiency Below Threshold. This code is reported on Yanmar equipment running the described engine family.
Can I keep working with Yanmar code P20EE?
Limited operation only -- finish the current task then shut down for repair.
How much does Yanmar P20EE cost to fix?
Typical repair cost: $300-$3,500. Off-road diesel shop labor runs $125-$175/hr in 2026. Dealer diagnostic software (Yanmar SmartAssist / YDT) is usually required.
P20EE on Other Platforms
The same code ID appears across other engines, vehicles, and equipment. Diagnostic flow varies by platform — see the matching breakdown: