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2018 Range Rover Sport HSE - P0420 Code and Reduced Power

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Mike T. · rep 0 · May 25, 4:41 AM · 1 replies · solved · Question

Vehicle: 2018 Land Rover Range Rover Sport HSE

My 2018 Range Rover Sport HSE has the check engine light on, and I scanned it to get a P0420 code. I've also noticed a slight decrease in power, especially when accelerating, and sometimes a faint, sulfur-like smell from the exhaust.

Is this definitely a catalytic converter issue, or could it be something else like a faulty O2 sensor that's tricking the system? I'm trying to figure out if this is a DIY fix or if I need to brace for a big repair bill.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:41 AM

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ClearTheCode admin answer: The P0420 code (Catalyst System Efficiency Below Threshold Bank 1) indicates that your vehicle's catalytic converter isn't operating as efficiently as it should be. While it points to the catalytic converter, other issues can trigger this code.

Here are the common causes and diagnostic steps:

  1. Exhaust Leaks: Check for any leaks in the exhaust system upstream of the catalytic converter. Even small leaks can cause the O2 sensors to read incorrectly.
  2. Oxygen Sensors: A faulty upstream or downstream O2 sensor can provide incorrect readings, leading the PCM (Powertrain Control Module) to believe the catalytic converter is failing. You can monitor sensor data with a good scan tool.
  3. Catalytic Converter Failure: Over time, catalytic converters can become clogged or damaged, reducing their efficiency. The sulfur smell is a strong indicator of a failing cat.
  4. Engine Misfires or Rich/Lean Conditions: Persistent misfires or issues with fuel delivery (running too rich or too lean) can damage the catalytic converter over time by sending unburnt fuel into it.

When to see a shop:

  • If you lack the tools or expertise to diagnose exhaust leaks or O2 sensor function.
  • If the issue persists after basic checks, as replacing a catalytic converter is a significant repair requiring specialized tools and knowledge.
  • If you notice significant performance loss, excessive exhaust smell, or other warning lights, as continued driving with a failing catalytic converter can damage other engine components.
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