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2019 Pathfinder SL exhaust smell and P0420 code

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Chris P. · rep 0 · May 25, 1:54 AM · 1 replies · solved · Question

Vehicle: 2019 Nissan Pathfinder SL

My 2019 Nissan Pathfinder SL, with about 60,000 miles, recently started having a noticeable exhaust smell, especially when idling or at low speeds. It's a bit like rotten eggs. The check engine light came on a few days ago, and when I had it scanned at an auto parts store, it pulled a P0420 code.

I'm guessing it's the catalytic converter, but I'm hoping it's something less expensive. The car still drives fine, no noticeable loss of power, but the smell is really annoying. What are my options here?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 1:54 AM

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  1. Initial Diagnosis: The combination of a "rotten egg" smell (sulfur) and a P0420 diagnostic trouble code (Catalyst System Efficiency Below Threshold Bank 1) strongly indicates an issue with your 2019 Nissan Pathfinder's catalytic converter, specifically on Bank 1.
  2. Common Causes:
    • Failing Catalytic Converter: The most common cause of a P0420 code is a failing catalytic converter. Over time, the internal catalyst material can degrade, becoming less efficient at converting harmful exhaust gases. The rotten egg smell is often due to sulfur compounds not being properly converted.
    • Oxygen (O2) Sensor Malfunction: While less common, a faulty upstream or downstream O2 sensor can sometimes trigger a P0420 code by sending incorrect readings to the ECU, making it seem like the converter is inefficient. However, the exhaust smell points more directly to the converter itself.
    • Exhaust Leaks: Leaks in the exhaust system before or near the O2 sensors can affect readings and potentially trigger a P0420, but typically also come with a loud exhaust noise.
    • Engine Misfires/Running Rich: Persistent engine misfires or an engine running excessively rich (too much fuel) can overload and damage the catalytic converter over time, leading to its premature failure.
  3. When to See a Shop:
    • Prompt Inspection: While your Pathfinder might drive fine now, a failing catalytic converter is an emissions control device, and it's important to address it. Driving with a P0420 can eventually lead to reduced fuel economy or, in severe cases, a clogged converter that restricts exhaust flow, causing power loss.
    • Professional Diagnostic: Take your vehicle to a reputable mechanic. They will confirm the P0420 code and perform further diagnostics:
      • O2 Sensor Check: They'll monitor live data from the upstream and downstream O2 sensors to compare their readings and determine if the sensors themselves are functioning correctly or if the converter truly isn't doing its job.
      • Exhaust System Inspection: They will check for any exhaust leaks that could be influencing the O2 sensor readings or causing the smell.
      • Backpressure Test: In some cases, a backpressure test can confirm if the converter is clogged.
    • Repair Options: If the catalytic converter is indeed failing, replacement is typically the solution. Ensure any replacement part is compliant with local emissions regulations. Addressing the root cause if it was an engine issue (like misfires) is also crucial to prevent recurrence.
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