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DEF System Malfunction on my 2022 Ram 3500 Diesel - P20EE Code

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David L. · rep 0 · May 25, 2:34 AM · 1 replies · solved · Question

Vehicle: 2022 Ram 3500 Laramie (Cummins Diesel)

Hey everyone, I'm having issues with the DEF system on my 2022 Ram 3500 with the Cummins diesel. The 'Check Engine' light came on, along with a 'Service DEF System' message, and I'm getting the dreaded countdown to limp mode. When I scanned it, I got a P20EE code: 'NOx Catalyst Efficiency Below Threshold (Bank 1)'.

I've kept up with my DEF fluid, always using quality brand. This truck only has 45k miles on it, so I'm pretty frustrated. Is this a common problem for the newer Ram diesels? What usually causes this code?

I'm worried about getting stuck in limp mode, especially since I use this truck for towing. What should I be looking at, and what's the typical repair for this? Any advice on how to avoid this in the future would be great.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:34 AM

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ClearTheCode admin answer:

The P20EE code on your 2022 Ram 3500 Cummins indicates an issue with the Selective Catalytic Reduction (SCR) system's efficiency, specifically related to NOx reduction. This is a common and often frustrating problem in modern diesel trucks, designed to meet strict emissions standards.

  1. Common Causes for P20EE:

    • NOx Sensor Failure: This is a very common culprit. The NOx sensors (pre- and post-SCR) monitor the effectiveness of the DEF system. If one fails or gives inaccurate readings, it can trigger P20EE.
    • DEF Doser Valve (Injector) Issues: A clogged or malfunctioning DEF doser valve can prevent the correct amount of DEF from being injected into the exhaust stream, leading to insufficient NOx reduction.
    • Contaminated or Low-Quality DEF: While you mentioned using quality DEF, even a single batch of contaminated or improperly stored fluid can cause issues. Ensure the DEF is fresh and stored correctly.
    • SCR Catalyst Failure: Less common, but the SCR catalyst itself can become fouled or degrade over time, reducing its efficiency.
    • Exhaust Leaks: Leaks in the exhaust system upstream of the SCR can affect sensor readings and system performance.

  2. Diagnostics & Action:

    • Scan Tool Data: A professional scan tool can read live data from the NOx sensors, DEF pressure, and doser operation, which is crucial for diagnosis.
    • Visual Inspection: Check for any visible leaks in the DEF lines or exhaust system.
    • DEF Quality Test: Some shops can test the quality of your DEF fluid.

  3. When to See a Shop:

    • Given the P20EE code and the 'Service DEF System' message, it is critical to take your truck to a qualified diesel mechanic or Ram dealership immediately. The countdown to limp mode means the engine's power will be severely limited soon, making it unsafe and impractical for towing.
    • Ignoring this issue can lead to more severe problems and costly repairs down the line. Repairs can range from replacing a NOx sensor ($300-$800+) to a DEF doser ($500-$1000+) or even the SCR catalyst itself (potentially thousands of dollars). Early diagnosis can save you significant expense and prevent being stranded.
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