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2016 Ram 1500 EcoDiesel - P20EE and P20E8 - DEF System Issues

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

Vehicle: 2016 Ram 1500 EcoDiesel Outdoorsman

My 2016 Ram 1500 EcoDiesel (Outdoorsman trim) is giving me trouble with the DEF system. I've got a Check Engine Light, and my scanner shows codes P20EE (SCR NOx Catalyst Efficiency Below Threshold) and P20E8 (Reductant Pressure Sensor Circuit Low).

I've noticed the DEF gauge sometimes acts erratically, and I'm concerned about potential derate if this continues. The truck has about 95,000 miles. I usually fill up the DEF tank when it gets low with BlueDEF. What could be causing these codes, and what's the best way to tackle this without breaking the bank?

✓ Accepted solution

ClearTheCode Admin

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

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ClearTheCode admin answer:

  1. Understanding DEF System Codes (P20EE, P20E8): These codes indicate issues with your EcoDiesel's Selective Catalytic Reduction (SCR) system, which uses Diesel Exhaust Fluid (DEF) to reduce NOx emissions. P20EE points to the SCR catalyst not performing efficiently, often due to issues with DEF injection or the catalyst itself. P20E8 specifically points to a low pressure reading from the reductant (DEF) pressure sensor, suggesting a problem with DEF delivery or the sensor itself.

  2. Initial Diagnostic Steps:

    • Check DEF Level and Quality: Ensure your DEF tank is full and that you're using fresh, high-quality DEF. Old or contaminated DEF can crystallize and cause issues. If unsure, drain and refill with fresh DEF.
    • Inspect DEF Injector: The DEF injector (doser valve) can get clogged with crystallized DEF. Locate it in the exhaust system and inspect it for blockages. Sometimes, a cleaning might help, but often replacement is needed if it's severely clogged.
    • Examine DEF Pump and Lines: The P20E8 code points to pressure issues. Check the DEF pump for proper operation (you might hear it prime) and inspect the DEF lines for any leaks, blockages, or damage. Crystallization inside the lines can restrict flow.
    • Check Reductant Pressure Sensor: This sensor is crucial for the system to monitor DEF pressure. It could be faulty, providing inaccurate readings. Its location is typically near the DEF pump or in the DEF tank module.

  3. Common Causes for DEF System Faults:

    • Crystallization or contamination of DEF.
    • Faulty or clogged DEF injector (doser valve).
    • Failure of the DEF pump.
    • Blocked or leaking DEF lines.
    • Faulty Reductant Pressure Sensor.
    • Failure of the NOx sensors (upstream or downstream of the SCR catalyst).
    • Internal failure of the SCR catalyst itself (less common, but possible with prolonged issues).

  4. When to See a Professional Shop:

    • If you've checked the basic DEF level, quality, and injector for obvious blockages, and the codes persist.
    • If the DEF system initiates a 'derate' condition, where engine power is significantly reduced to prevent further emissions violations. Driving in derate can be very inconvenient and the issue needs immediate attention.
    • Diagnosing DEF system issues often requires specialized scan tools to monitor DEF pressure, temperature, and NOx sensor readings, which a professional shop will have. They can accurately pinpoint whether the issue is a sensor, pump, injector, or the catalyst itself.
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