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2020 Ram 2500 Diesel - P20EE Code and DEF System Warning

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Melissa G. · rep 0 · May 22, 3:36 AM · 1 replies · solved · Question

Vehicle: 2020 Ram 2500 Laramie

Hey everyone, I've got a 2020 Ram 2500 Laramie with the 6.7L Cummins diesel. Recently, my check engine light came on, and I'm getting a "Service DEF System - See Dealer" message on the dash. I pulled the code with my scanner, and it's showing P20EE - "NOx Sensor Performance - Bank 1 Sensor 1."

I've been pretty good about using quality DEF and not letting it run low. The truck seems to be running fine otherwise, no noticeable power loss or anything. What's usually the culprit with this code on these trucks? Is it likely a bad NOx sensor, or could it be something else in the DEF system like the heater or pump?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:36 AM

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ClearTheCode admin answer:

The P20EE code on your 2020 Ram 2500 with the 6.7L Cummins diesel indicates an issue with the NOx (Nitrogen Oxide) sensor performance, specifically Bank 1 Sensor 1, which is typically the upstream sensor before the SCR (Selective Catalytic Reduction) catalyst. This is a common code on modern diesel trucks and points directly to your emissions system.

Here's a breakdown of common causes and what to check:

  1. Faulty NOx Sensor: This is the most frequent culprit. NOx sensors are critical for monitoring exhaust gas composition and ensuring the SCR system is effectively reducing emissions. They can fail due to heat, contamination, or electrical issues. A failing sensor might send incorrect readings, triggering the P20EE code.
  2. DEF Quality/Contamination: While you mentioned using quality DEF, even a single batch of contaminated or expired DEF can cause issues. The DEF system relies on precise chemical reactions. If the DEF isn't pure, it can lead to inefficient NOx reduction and sensor errors.
  3. DEF Injector Issues: The DEF injector sprays DEF into the exhaust stream. If it's clogged, leaking, or not spraying correctly, the SCR system won't function optimally, which can indirectly lead to NOx sensor performance codes.
  4. SCR Catalyst Efficiency: Less common, but a degraded or damaged SCR catalyst itself could lead to the NOx sensor reporting poor performance because the catalyst isn't doing its job.
  5. Wiring/Electrical Issues: Always check the wiring harness and connectors to the NOx sensor for any signs of damage, corrosion, or loose connections.

Diagnostic Steps:

  • Visual Inspection: Check the NOx sensor wiring and connectors for damage.
  • DEF System Check: Ensure your DEF tank is full and the DEF fluid is fresh. If you suspect contamination, draining and refilling with fresh, high-quality DEF might be a first step, though this is less likely if the code specifically points to sensor performance.

When to See a Shop:

  • Given the specific code, a professional diagnosis is highly recommended. They can use advanced scan tools to monitor live NOx sensor data, check DEF pressure, and perform system tests to pinpoint the exact failure. Often, replacing the upstream NOx sensor resolves this issue. Ignoring this code can lead to a derate in engine power or even prevent the truck from starting.
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