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DEF System Warning & Derate on 2020 Ram 2500 Cummins

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Sarah K. · rep 0 · May 22, 3:37 AM · 1 replies · solved · Question

Vehicle: 2020 Ram 2500 Laramie

I'm having a major headache with my 2020 Ram 2500 Laramie with the 6.7L Cummins diesel. I've been getting 'Service DEF System' warnings, and now it's telling me 'Speed Limited to 5 MPH in 200 Miles'. I've tried refilling the DEF tank, but the warnings persist. I also noticed a check engine light.

I hooked up my OBD scanner and pulled codes P20EE and P20E8. This is really frustrating, especially since the truck isn't that old. Is this a common problem with these Cummins engines? What's the typical fix, and is there a TSB for it? I rely on this truck for work, so I need to get it sorted out quickly.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:37 AM

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ClearTheCode admin answer:

Unfortunately, DEF (Diesel Exhaust Fluid) system issues are a known concern for many modern diesel trucks, including the 6.7L Cummins in your 2020 Ram 2500. The codes P20EE (SCR NOx Catalyst Efficiency Below Threshold) and P20E8 (Reductant Pressure Sensor Circuit Low) strongly indicate a problem within your Selective Catalytic Reduction (SCR) system, which is crucial for emissions control.

Here's a breakdown of potential causes and steps:

  1. Common Causes:
    • DEF Quality/Contamination: Using old, contaminated, or non-compliant DEF can crystallize and clog the system.
    • DEF Injector Issues: The DEF injector can become clogged or fail, preventing proper DEF atomization into the exhaust stream.
    • NOx Sensors: Faulty upstream or downstream NOx sensors can provide incorrect readings, leading the ECM to believe the SCR system isn't working efficiently.
    • DEF Pump/Heater: A failing DEF pump or heater element can prevent DEF from being delivered or properly thawed in cold weather.
    • SCR Catalyst Failure: Less common, but the catalyst itself can degrade or become contaminated.
  2. TSBs/Recalls: There have been various TSBs and even recalls related to DEF systems and emissions components on Ram Cummins trucks. It's crucial to check with a dealership using your VIN to see if your truck is eligible for any outstanding service actions.
  3. Troubleshooting & Repair:
    • Professional Diagnosis: Given the derate warning, a professional diagnosis is essential. A dealership or a diesel specialist will have advanced diagnostic tools to pinpoint the exact component failure.
    • Component Replacement: Depending on the diagnosis, common repairs include replacing the DEF injector, NOx sensors, DEF pump, or even the entire DEF tank assembly if the heater or level sensor is integrated and failed.
    • Software Updates: Sometimes, a software update can resolve certain DEF system glitches.
  4. When to See a Shop: Immediately. The 'Speed Limited to 5 MPH' warning is a critical indicator. Continuing to drive could lead to a complete derate, leaving you stranded. Do not delay in getting this addressed by a qualified technician.
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