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2019 Crosstrek P0420 Check Engine Light

0

Mike T. · rep 0 · May 25, 2:14 AM · 1 replies · solved · Question

Vehicle: 2019 Subaru Crosstrek 2.0i Limited

Hello Subaru community, I'm hoping for some advice. My 2019 Subaru Crosstrek 2.0i Limited, with about 60,000 miles, just threw a check engine light. I scanned it with my OBD-II reader, and it's showing code P0420: Catalyst System Efficiency Below Threshold (Bank 1).

The car seems to be running fine, no noticeable loss of power, no strange noises, and fuel economy seems normal. I'm trying to figure out if this is something I need to address immediately or if it could be a simple fix like an O2 sensor. What's the typical cause for this code on a Crosstrek?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:14 AM

0

ClearTheCode admin answer:

The P0420 code on your 2019 Subaru Crosstrek indicates that the catalytic converter's efficiency is below the acceptable threshold. While the car may seem to run fine, this code should be addressed to ensure proper emissions control and prevent potential long-term issues.

Possible Causes:

  1. Failing Catalytic Converter: The most common cause. Over time, the catalyst material inside the converter can degrade, reducing its ability to convert harmful exhaust gases. This is usually due to age, high mileage, or exposure to unburnt fuel (e.g., from prolonged misfires).
  2. Faulty Oxygen (O2) Sensors:
    • Upstream O2 Sensor: Monitors the air-fuel ratio. A malfunctioning upstream sensor can send incorrect data, leading the engine to run too rich or too lean, which can damage the catalytic converter.
    • Downstream O2 Sensor: Monitors the efficiency of the catalytic converter. If this sensor is faulty, it might incorrectly report low efficiency even if the cat is fine. However, it's less common for a P0420 to be just a downstream O2 sensor issue without other codes.
  3. Exhaust Leaks: A leak in the exhaust system before or between the O2 sensors can allow unmetered air in, skewing sensor readings and triggering a P0420.
  4. Engine Misfires/Running Rich: Persistent engine misfires or an engine running excessively rich can introduce unburnt fuel into the catalytic converter, causing it to overheat and degrade prematurely.

When to See a Shop:

  • Soon: While not an immediate emergency if the car is running fine, you should get it diagnosed within a few weeks. Driving with a P0420 can lead to failing emissions tests and potentially more severe damage if the underlying cause (like misfires) is not addressed.
  • Immediately: If you notice a significant drop in fuel economy, a sulfur smell (rotten eggs) from the exhaust, or a noticeable loss of power, have it checked right away.

What a Shop Will Do:

  1. Diagnostic Scan and Freeze Frame Data: Analyze the P0420 code and any associated freeze frame data to understand the conditions when the code set.
  2. O2 Sensor Readings: Monitor live data from both upstream and downstream O2 sensors to compare their waveforms and determine if they are functioning correctly.
  3. Exhaust System Inspection: Check for any exhaust leaks, especially around the catalytic converter and O2 sensor bungs.
  4. Engine Performance Check: Rule out other issues like misfires, fuel system problems, or vacuum leaks that could contribute to the P0420.
  5. Recommendations: Based on the diagnosis, they might recommend replacing an O2 sensor, repairing an exhaust leak, or, if confirmed, replacing the catalytic converter.
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