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Check Engine Light & Reduced Power on 2020 Ram 2500 Diesel - DEF System?

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Sarah K. · rep 0 · May 25, 2:32 AM · 1 replies · solved · Question

Vehicle: 2020 Ram 2500 Laramie

My 2020 Ram 2500 Laramie with the 6.7L Cummins just threw a Check Engine Light, and now I'm getting a 'Reduced Power' message on the dash. I'm pretty sure it's related to the DEF (Diesel Exhaust Fluid) system because I've been getting warnings about low DEF lately, even though I just filled it up.

I've heard these DEF systems can be problematic. Is there anything I can check myself before taking it to the dealer? I'm worried about getting stranded or having to pay for a huge repair. The truck has about 75,000 miles on it.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:32 AM

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ClearTheCode admin answer:

It's very common for Ram Cummins diesel trucks to experience issues with the Diesel Exhaust Fluid (DEF) system, especially around your mileage. The 'Reduced Power' message, often called 'limp mode,' is typically triggered by DEF system faults to prevent emissions violations.

Common Causes & DIY Checks:

  1. DEF Quality/Contamination: Ensure you're using fresh, high-quality DEF. Contaminated or old DEF can crystallize and cause sensor or injector blockages. If you recently filled up, consider if the DEF source was reliable.
  2. DEF Level Sensor: These sensors can fail, incorrectly reporting low DEF even when the tank is full. There's no easy DIY check for this without specialized tools.
  3. DEF Injector Clogging: The DEF injector sprays fluid into the exhaust stream. If it gets clogged with crystallized DEF, it won't atomize properly. Sometimes, removing and cleaning the injector can help, but it requires careful handling.
  4. DEF Heater Failure: In colder climates, the DEF tank has a heater to prevent freezing. If this fails, the system won't work correctly, especially in winter. This often triggers specific fault codes.
  5. NOx Sensors: Your truck has multiple NOx (Nitrogen Oxide) sensors. If one fails or gives inaccurate readings, it can trigger DEF-related codes.

Common OBD-II Codes:

  • P20EE: SCR NOx Catalyst Efficiency Below Threshold (Bank 1)
  • P207F: Reductant Quality Performance
  • P20C2: Reductant Heater 'A' Control Circuit
  • P203F: Reductant Level Sensor Circuit High

When to See a Shop: While some basic checks can be done, DEF system issues are often complex and require specialized diagnostic tools to pinpoint the exact failing component. Given the 'Reduced Power' mode, it's strongly recommended to visit a Ram dealership or a diesel specialist as soon as possible. They can:

  • Read specific DEF system fault codes (which are often manufacturer-specific).
  • Perform diagnostic tests on the DEF pump, injector, heaters, and sensors.
  • Perform a forced DEF system regeneration if applicable.
  • Replace faulty components and clear the codes properly. Ignoring these warnings can lead to further issues or extended periods in limp mode.
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