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2018 Outlander GT - P0420 Code and Check Engine Light

0

Mike T. · rep 0 · May 25, 4:05 AM · 1 replies · solved · Question

Vehicle: 2018 Mitsubishi Outlander GT

Hey everyone,

My 2018 Mitsubishi Outlander GT, with about 85,000 miles, recently threw a check engine light. I used my OBD-II scanner and it's showing a P0420 code: 'Catalyst System Efficiency Below Threshold (Bank 1)'.

The car seems to be running fine, no noticeable loss of power or strange noises. Fuel economy might be slightly worse, but it's hard to tell for sure. I've heard this could be anything from a bad O2 sensor to a failing catalytic converter.

Has anyone else experienced this with their Outlander? What was the fix? I'm trying to figure out if this is something I can tackle myself or if I need to brace for a big repair bill. Any advice on diagnostics would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:05 AM

0

ClearTheCode admin answer:

The P0420 code on your 2018 Mitsubishi Outlander GT indicates that the catalytic converter's efficiency is below the required threshold. While it often points to a failing catalytic converter, there are several other potential causes that should be investigated first.

Common Causes for P0420:

  1. Oxygen Sensors: Failing upstream or downstream O2 sensors can send incorrect data to the ECU, leading it to falsely believe the catalytic converter is inefficient. The downstream (post-cat) sensor is particularly critical for monitoring converter performance.
  2. Exhaust Leaks: Leaks in the exhaust system before or near the catalytic converter can allow unmetered air in, affecting O2 sensor readings and triggering the code.
  3. Engine Misfires or Rich/Lean Conditions: Persistent engine problems like misfires, faulty fuel injectors, or a bad mass airflow sensor can cause unburnt fuel or incorrect air-fuel mixtures to enter the catalytic converter, overheating it and reducing its lifespan.
  4. Faulty Catalytic Converter: Over time, catalytic converters can become clogged or internally damaged, losing their ability to properly convert harmful exhaust gases.

Diagnostic Steps:

  1. Check for Exhaust Leaks: Visually inspect the exhaust system for any cracks, holes, or loose connections. A smoke test can also identify hard-to-find leaks.
  2. Monitor O2 Sensor Data: Using a professional scan tool, monitor the live data for both upstream and downstream oxygen sensors. The upstream sensor should fluctuate rapidly, while the downstream sensor should show a relatively steady voltage, lower than the upstream, indicating the converter is working. If the downstream sensor mirrors the upstream, the converter is likely inefficient.
  3. Inspect for Misfires/Engine Issues: Check for any other stored or pending engine codes that might indicate an underlying engine problem contributing to the P0420.
  4. Fuel System Check: Ensure fuel pressure is correct and injectors are spraying properly.

When to See a Shop: If you're not comfortable performing these diagnostic steps, or if initial checks don't reveal an obvious cause, it's best to take your Outlander to a qualified mechanic. They have specialized tools and expertise to accurately diagnose the root cause of the P0420 code. Addressing the issue promptly can prevent further damage to your exhaust system or engine components.

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