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2017 Ram 2500 Cummins DEF System Warning - What to Check?

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Mike T. · rep 0 · May 25, 2:34 AM · 1 replies · solved · Question

Vehicle: 2017 Ram 2500 Laramie

Hello Ram owners,

I'm reaching out about an issue with my 2017 Ram 2500 Laramie, equipped with the 6.7L Cummins engine. Recently, I've been getting the dreaded "Service DEF System" warning message on my dash. Sometimes it's followed by a countdown to limp mode, which is incredibly stressful, especially when towing.

I've already tried refilling the DEF tank with fresh, high-quality fluid, but the message keeps coming back. The truck has about 85,000 miles on it. What are the most common culprits for DEF system malfunctions on these trucks? Is there anything I can realistically check myself before having to take it into the dealership for an expensive diagnosis and repair?

Any insights or tips from those who've dealt with this would be a huge help!

✓ Accepted solution

ClearTheCode Admin

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

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ClearTheCode admin answer:

The "Service DEF System" warning on your 2017 Ram 2500 Cummins is a common, albeit frustrating, issue. The Diesel Exhaust Fluid (DEF) system is complex, and several components can lead to this warning. Here's a breakdown of what to investigate and common causes:

  1. Check for Common OBD-II Codes:

    • P20EE: SCR NOx Catalyst Efficiency Below Threshold (Bank 1)
    • P207F: Reductant Quality Performance
    • P208E: Reductant Injection Valve Stuck Open
    • P204F: Reductant System Performance
    • P20BA: Reductant Heater A Control Circuit Performance
    • These codes can point to specific component failures within the DEF system.

  2. Inspect DEF Tank and Lines for Crystallization:

    • DEF can crystallize if exposed to air or if the system's heaters fail in cold weather. Look for white, crystalline deposits around the DEF tank cap, lines, and especially the DEF injector (located in the exhaust stream).
    • Crystallization can clog lines, filters, and the injector, preventing proper DEF delivery.

  3. Evaluate DEF Injector:

    • A clogged or faulty DEF injector (doser valve) is a frequent cause of issues. If it's not spraying DEF correctly, the Selective Catalytic Reduction (SCR) system won't function, leading to warnings.
    • Visually inspect the injector for residue or blockages. Cleaning it can sometimes resolve the issue, but often replacement is necessary.

  4. Consider DEF Quality and Age:

    • Even if you just refilled, ensure the DEF you used wasn't expired or contaminated. DEF has a shelf life, usually about 1-2 years, and can degrade if stored improperly.

  5. Examine DEF Heaters and Sensors:

    • The DEF tank contains heaters to prevent the fluid from freezing. If these fail, especially in cold climates, the system won't work. Sensors within the tank (level, temperature, quality) can also fail, sending incorrect data to the ECU.

Common Causes:

  • Crystallization/Clogging: The most frequent issue, often due to faulty heaters or improper DEF storage/usage.
  • Faulty DEF Injector: The injector can clog or fail electronically.
  • DEF Quality Sensor Failure: The sensor that checks DEF quality can malfunction.
  • NOx Sensor Failure: While part of the exhaust system, faulty NOx sensors (pre or post SCR) can trigger DEF-related codes because they monitor the effectiveness of the DEF injection.

When to See a Shop: Given the complexity and the potential for limp mode, it's highly recommended to take your truck to a dealership or a diesel specialist if you're getting persistent warnings after basic checks. They have specialized diagnostic tools to pinpoint the exact component failure within the DEF system. Ignoring these warnings can lead to permanent damage to the SCR catalyst, which is a very costly repair.

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