DEF System Warning on 2017 Ram 2500 EcoDiesel - P20EE Code

The P20EE code on your 2017 Ram 2500 EcoDiesel is indeed a common issue related to the Selective Catalytic Reduction (SCR) system and NOx emissions. It indicates that the system isn't reducing NOx emissions efficiently enough.

Here's a breakdown of common causes and steps:

1. DEF Quality/Contamination: Even if you use quality fluid, contamination can occur. Ensure your DEF is fresh and stored properly. If you recently refilled, it's possible the fluid was old or contaminated. Sometimes, draining and refilling with fresh, high-quality DEF can help.
2. NOx Sensors: Your truck has multiple NOx sensors (upstream and downstream of the SCR catalyst). A faulty sensor can send incorrect readings, triggering the P20EE code. This is a very common failure point.
3. DEF Injector (Doser Valve): The DEF injector sprays DEF into the exhaust stream. If it's clogged or malfunctioning, it won't atomize the DEF properly, leading to inefficient NOx reduction. Carbon buildup is a frequent cause.
4. SCR Catalyst: While less common at 75,000 miles, the SCR catalyst itself can become fouled or fail, especially if there have been long-standing issues with DEF quality or injector performance.
5. Wiring/Electrical Issues: Check for any visible damage to the wiring harnesses connected to the NOx sensors or DEF injector.

When to See a Shop: Given the complexity of the DEF system and the potential for limp mode, it's highly recommended to have a professional diagnose this. A dealership or a diesel specialist will have advanced diagnostic tools to monitor NOx sensor readings, test the DEF injector, and perform system resets or software updates. Attempting to clear the code without addressing the root cause will likely result in its return, and you risk entering a severe limp mode that limits vehicle speed and power.