SCR NOx Catalyst Efficiency Below Threshold
The MAXXFORCE-P20EE-11 (MaxxForce) diesel fault code means: SCR NOx Catalyst Efficiency Below Threshold. This is a serious severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- advanced
- Estimated cost
- $500-$6,500
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Common Symptoms
- CEL
- Countdown to derate
- Reduced MPG
Probable Causes (Ranked by Likelihood)
- DEF quality poor or diluted Likely
- Failed NOx inlet or outlet sensor Likely
- Degraded SCR catalyst Possible
Step-by-Step Diagnostic Procedure
Test DEF concentration with refractometer (32.5% urea).
Read NOx sensor values at steady cruise.
Replace sensors before replacing SCR.
Frequently Asked Questions
What is P20EE on a MaxxForce 11 (10.5L)?
P20EE on a MaxxForce 11 (10.5L) (2008-2014) indicates: SCR NOx Catalyst Efficiency Below Threshold. This is a known fault code on the MaxxForce engine family and typically points to the causes listed above.
Can I drive with P20EE on my MaxxForce?
Only drive short distances to reach a repair facility. Continued operation may cause further damage or progressive derate.
How much does it cost to fix MaxxForce P20EE?
Repair cost is typically $500-$6,500 depending on the underlying cause and shop rate. Many MaxxForce faults (especially EGR cooler, head bolt, and VGT repairs) are major expenses that drove fleet owners to repower with Cummins or retire these trucks early.