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2020 Ram 2500 Cummins - DEF System Malfunction P20EE

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Mike T. · rep 0 · May 25, 2:26 AM · 1 replies · solved · Question

Vehicle: 2020 Ram 2500 Laramie Cummins

Hello Ram community,

I'm having an issue with my 2020 Ram 2500 Cummins. The check engine light came on, and I'm getting a 'Service DEF System' message on the dash. My OBD-II scanner is showing a P20EE code, which points to an SCR NOx Catalyst Efficiency issue.

The truck has about 60,000 miles, and I've always used good quality DEF. I'm worried about going into limp mode, as I use this truck for towing fairly often. It seems to be running fine otherwise, but that warning is concerning.

Has anyone else experienced this specific code on their Cummins? What was the fix? Is this something I can troubleshoot myself, or am I looking at a costly dealership visit?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:26 AM

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ClearTheCode admin answer: The P20EE code on your 2020 Ram 2500 Cummins indicates that the Selective Catalytic Reduction (SCR) system's NOx catalyst efficiency is below threshold. This is a common issue with modern diesel vehicles and their complex emissions systems. Here's what you should investigate:

  1. DEF Quality and Level:

    • Cause: Even if you use 'good quality' DEF, contamination or expired DEF can cause this code. Ensure your DEF tank is full, and if you suspect contamination, you might need to drain and refill with fresh, high-quality DEF. The DEF system relies on precise urea concentration.

  2. NOx Sensors:

    • Cause: There are typically two NOx sensors (upstream and downstream of the SCR catalyst). If either sensor is faulty, it can provide incorrect readings, leading the PCM to believe the SCR system isn't working efficiently. These sensors are critical for monitoring emissions performance and are a common failure point.

  3. DEF Injector (Doser Valve):

    • Cause: The DEF injector sprays urea into the exhaust stream. If it's clogged, faulty, or not spraying correctly, the SCR system won't function as intended. Deposits can build up over time, especially if the engine isn't allowed to reach full operating temperature often.

  4. DEF Heater and Pump Assembly:

    • Cause: The DEF system has heaters to prevent the DEF from freezing and a pump to deliver it. A failure in either of these components can prevent DEF from reaching the SCR, triggering the P20EE code. Check for related codes like P203F (DEF fluid quality) or P20C2 (DEF pump performance).

  5. SCR Catalyst Itself:

    • Cause: In rarer cases, the SCR catalyst itself can become damaged or contaminated, losing its ability to convert NOx gases. This is usually a more expensive repair.

When to See a Shop: Given the complexity of diesel emissions systems and the potential for limp mode, it's highly recommended to have a diesel specialist or dealership diagnose this. They have specialized diagnostic tools to monitor NOx sensor readings, DEF pressure, and injector operation, which are crucial for accurately pinpointing the root cause of P20EE. Driving extensively with this code can lead to further issues or forced derates.

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