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2017 CR-V Check Engine Light with P0420 - Catalyst System

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Mike T. · rep 0 · May 25, 1:45 AM · 1 replies · solved · Question

Vehicle: 2017 Honda CR-V EX-L

Hey everyone,

My 2017 Honda CR-V EX-L, with about 85,000 miles, just 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 driving fine, no noticeable loss of power or strange noises, and fuel economy hasn't taken a huge hit. I'm a bit worried about what this could mean for my catalytic converter. Is there anything I can check myself before taking it to a shop?

Could it be just an O2 sensor, or am I looking at a much more expensive repair? Any advice on diagnosing this further would be greatly appreciated.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 1:45 AM

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ClearTheCode admin answer:

The P0420 code on your 2017 Honda CR-V indicates that the catalytic converter's efficiency is below the required threshold. While it often points to a failing catalytic converter, it's crucial to rule out other potential causes first.

Here are the steps for diagnosis and common causes:

  1. Verify the Code and Clear: Confirm the P0420 code with your scanner. Sometimes, a temporary issue can trigger it. Clear the code and drive for a few days to see if it returns.
  2. Inspect for Exhaust Leaks:
    • Listen for hissing or ticking sounds from the exhaust system, especially near the manifold or catalytic converter.
    • Visually inspect for cracks, rust, or loose connections. Leaks before or near the O2 sensors can cause false readings.
  3. Check Oxygen Sensors (O2 Sensors):
    • The P0420 code is often triggered by the difference in readings between the upstream (pre-cat) and downstream (post-cat) O2 sensors.
    • A faulty downstream O2 sensor can sometimes falsely report catalyst inefficiency. While harder to diagnose without specialized tools, a scanner capable of live data can show if the sensors are switching correctly. The downstream sensor should show a relatively steady voltage compared to the fluctuating upstream sensor if the catalyst is working.
  4. Engine Performance Issues:
    • Ensure there are no other underlying engine codes (misfires, rich/lean conditions) that could be sending unburnt fuel to the catalyst, causing it to overheat or fail prematurely. Address any misfire codes (P030x) first.
  5. Fuel Quality: Poor fuel quality or consistent short trips can sometimes impact catalyst efficiency over time.
  6. Catalytic Converter Condition: If all other components check out, the catalytic converter itself may be failing. This is a common wear item over time.

When to See a Shop:

  • If the code returns quickly after clearing.
  • If you lack the tools or experience to perform detailed O2 sensor diagnostics or exhaust leak checks.
  • If you notice any significant decrease in fuel economy, power loss, or a rotten egg smell from the exhaust (a sign of a severely failing cat). A professional can perform a backpressure test or more advanced O2 sensor analysis to confirm the catalyst's health.
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