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2018 CR-V Check Engine Light - P0420 Code - What's Next?

0

Sarah K. · rep 0 · May 22, 2:41 AM · 1 replies · solved · Question

Vehicle: 2018 Honda CR-V EX-L

Hey everyone,

My 2018 Honda CR-V EX-L just threw a check engine light yesterday. 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 driving fine, no noticeable loss of power or strange noises, but I'm worried about potential damage or failing emissions. I've heard this could be anything from an O2 sensor to the catalytic converter itself.

What are the common causes for this code on a CR-V of this generation? Is there anything I can check myself before taking it to a shop? Any advice would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 2:41 AM

0

ClearTheCode admin answer:

The P0420 code on your 2018 Honda CR-V indicates that the catalytic converter's efficiency is below the required threshold. While it can be a serious issue, it's not always an immediate catastrophic failure. Here's a breakdown of common causes and steps:

  1. Verify the Code and Clear (Temporarily): Double-check the code with your scanner. Sometimes, a temporary glitch can trigger it. Clearing the code and driving for a bit can help determine if it returns immediately or after a specific driving cycle.
  2. Common Causes for P0420:
    • Oxygen Sensors (O2 Sensors): Faulty upstream or downstream O2 sensors are a very common cause. The downstream sensor monitors the catalytic converter's efficiency. If it's reading incorrectly, it can falsely trigger P0420.
    • Exhaust Leaks: Leaks in the exhaust system before or near the O2 sensors can introduce unmetered air, affecting sensor readings.
    • Catalytic Converter Failure: Over time, catalytic converters can degrade due to age, contamination (e.g., from excessive oil burning, coolant leaks), or physical damage. This is often the most expensive fix.
    • Engine Misfires/Running Rich/Lean: Persistent engine issues that cause unburnt fuel or excessive fuel to enter the exhaust can damage the catalytic converter over time.
  3. DIY Checks (Limited):
    • Visually inspect your exhaust system for any obvious leaks, especially around the O2 sensors.
    • If you have an advanced scanner, you can monitor live O2 sensor data. The downstream sensor's voltage should be relatively stable compared to the fluctuating upstream sensor. If it mirrors the upstream sensor, the converter is likely inefficient.

When to See a Shop:

  • If the check engine light returns quickly after clearing, or if you notice any performance issues (reduced fuel economy, lack of power, sulfur smell from exhaust).
  • A professional shop can perform a backpressure test, smoke test for exhaust leaks, and more detailed O2 sensor diagnostics to pinpoint the exact cause. They can also confirm if the catalytic converter itself needs replacement, which is a significant repair.
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