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2020 Ram 2500 Cummins DEF System Warnings and Limp Mode

0

Mike T. · rep 0 · May 25, 2:27 AM · 1 replies · solved · Question

Vehicle: 2020 Ram 2500 Longhorn

Hello Ram community,

I'm experiencing some concerning issues with the Diesel Exhaust Fluid (DEF) system on my 2020 Ram 2500 Longhorn with the 6.7L Cummins engine. Recently, I've been getting 'DEF System Malfunction' messages, followed by a countdown to limp mode. It's incredibly frustrating, especially when I'm towing.

The check engine light has also come on. I've tried topping off the DEF, but the warnings persist. I'm worried about getting stranded or damaging something more serious.

Has anyone with a 2020 or similar year Ram 2500/3500 Cummins dealt with this? What was the fix? Any common culprits I should look into?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:27 AM

0

ClearTheCode admin answer:

DEF system malfunctions are unfortunately a common headache for modern diesel truck owners, and your 2020 Ram 2500 Cummins is no exception. The system is complex, and many components can trigger these warnings and the dreaded limp mode countdown. Here are the most common causes:

  1. Clogged DEF Injector: Over time, the DEF injector can crystallize and become clogged, preventing proper DEF delivery into the exhaust stream. This leads to high NOx emissions and triggers warnings.
  2. Faulty NOx Sensors: Your truck has multiple NOx sensors (upstream and downstream). If one of these sensors fails or provides inaccurate readings, the system will believe there's a malfunction, even if DEF delivery is fine.
  3. DEF Quality Issues: While you topped off your DEF, sometimes using old or contaminated DEF can cause problems. Ensure you're using fresh, high-quality DEF from a sealed container.
  4. DEF Pump Failure: The DEF pump is responsible for drawing fluid from the tank and pressurizing it for injection. A failing pump will prevent DEF from reaching the injector.
  5. Heater Issues (Cold Weather): In colder climates, if the DEF tank heater or lines are not working, the DEF can freeze, leading to blockages and system faults.

Common OBD-II Codes:

  • P20EE: SCR NOx Catalyst Efficiency Below Threshold (Bank 1)
  • P207F: Reductant Quality Performance
  • P20E8: Reductant Pressure Too Low
  • P20A2: Reductant Heater 'A' Control Circuit/Open

When to See a Shop:

Given the complexity and the risk of limp mode, it's highly recommended to take your truck to a dealership or a specialist diesel shop as soon as possible. They have the diagnostic tools to read specific DEF system codes, perform active tests on components, and accurately pinpoint the failing part. Ignoring the countdown will eventually put your truck into a severely derated state, which can be dangerous if you're towing or driving on a highway.

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