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DEF System Warning & Check Engine Light on 2017 Ram 2500 Diesel

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Emily N. · rep 0 · May 22, 3:36 AM · 1 replies · solved · Question

Vehicle: 2017 Ram 2500 Laramie

Hello Ram community,

I'm having some trouble with my 2017 Ram 2500 Laramie with the 6.7L Cummins. Recently, I got a 'Service DEF System' warning, followed by a Check Engine Light. Now it's giving me a countdown to reduced power, which is really concerning. I checked the DEF tank, and it's full.

I pulled some codes with my OBD scanner: P20EE and P207F. I've heard these DEF systems can be problematic. What's usually the culprit here? Is this something I can tackle myself, or am I looking at a dealer visit?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:36 AM

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ClearTheCode admin answer:

The P20EE (SCR NOx Catalyst Efficiency Below Threshold) and P207F (Reductant Quality Performance) codes on your 2017 Ram 2500 Cummins are very common and point directly to issues within the Selective Catalytic Reduction (SCR) and Diesel Exhaust Fluid (DEF) system. These systems are critical for emissions control and can indeed trigger a power derate countdown.

Here are the common causes and steps:

  1. DEF Quality: Even if your tank is full, poor quality or contaminated DEF is a frequent cause. Ensure you're using fresh, certified DEF from a reputable source. DEF has a shelf life and can degrade if exposed to extreme temperatures or sunlight.
  2. DEF Injector: The DEF injector (doser valve) can become clogged or fail, preventing proper DEF atomization into the exhaust stream. This leads to inefficient NOx reduction and triggers the codes.
  3. NOx Sensors: Your truck has multiple NOx sensors (pre- and post-SCR catalyst). If one of these sensors fails or provides inaccurate readings, the ECM will detect an issue with SCR efficiency.
  4. DEF Heater/Level Sensor: The DEF tank contains a heater and level sensor. Failures in these components can prevent the system from operating correctly, especially in cold weather, and can also trigger related codes.
  5. SCR Catalyst: While less common, the SCR catalyst itself can become fouled or damaged, reducing its efficiency.

DIY Steps (Limited):

  • Drain and refill your DEF tank with fresh, high-quality DEF. Drive for a few cycles to see if the codes clear.
  • Inspect the DEF injector for crystallization or blockages (if accessible).

When to see a shop:

  • Given the power derate countdown and multiple codes, a professional diagnosis is highly recommended. A dealership or a diesel specialist will have advanced diagnostic tools to perform specific DEF system tests, monitor sensor readings, and pinpoint the exact failing component.
  • Replacing NOx sensors, DEF injectors, or DEF tank components often requires specialized tools and programming to ensure proper function and clear the codes effectively. Ignoring these warnings can lead to permanent damage to the SCR system or leave you stranded with severely reduced power.
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