Honda CR-V P0420 — Catalyst Efficiency Bank 1

Honda-specific code — factory diagnostic data

Last updated: May 14, 2026

Definition source: Honda factory description. Diagnostic guidance is based on factory-defined fault logic for this code.

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↗Looking for the cross-vehicle definition? Read the generic P0420 article for the SAE-defined fault logic that applies to all manufacturers.

P0420 Quick Answer

P0420 on a Honda CR-V is most often a genuine catalyst issue past 120k miles, a lazy rear O2 sensor under that threshold, or — on the 2017+ 1.5L turbo — a stuck-open thermostat (Honda TSB 19-103) preventing the engine from reaching full operating temperature. The 2.4L K24-equipped CR-Vs (2007-2016) tend to genuinely wear out their cats by 130k-150k miles.

What Does P0420 Mean on a Honda CR-V?

The Honda CR-V (2007-2024) stores P0420 when the PCM detects the condition described above. This guide focuses on the 2.4L i-VTEC / 1.5L L15B7 turbo — the most common configuration on this platform. Diagnostic priorities and likely root causes differ from the generic SAE definition because of platform-specific failure patterns documented below.

Symptoms

• Check Engine Light (P0420)
• No driveability symptoms
• Slight fuel economy reduction
• Sulfur smell under load (more common as cat degrades)
• On 1.5L turbo: long warm-up time before heater works = thermostat
• OBD-II / smog test failure

Common Causes (Most Likely on This Model First)

Order of likelihood on the CR-V P0420:

1. Worn catalyst substrate. The K24 2.4L CR-V cat is good for ~130k-150k miles on highway use, less on stop-and-go. The 1.5L turbo cat suffers more from oil dilution if the related TSB hasn’t been performed.
2. Rear (Bank 1 Sensor 2) O2 sensor lazy. Honda O2 sensors degrade after 100k miles. Switch speed slows, PCM reads the lazy response as cat storage loss.
3. Stuck-open thermostat (2017+ 1.5L turbo). TSB 19-103 — engine never reaches 180°F operating temp, catalyst monitor fails. Quick fix.
4. Oil dilution on 2017-2018 1.5L turbo (TSB 17-091). Fuel in oil drives consumption; oil mist contaminates the cat.
5. Bad upstream O2 sensor. Less common but a slow Sensor 1 can mis-report mixture, making the cat look worse than it is. Check sensor response time on a scan tool.

Diagnostic Approach

1. Check coolant temp at idle. If under 180°F sustained on the 1.5L turbo, suspect thermostat (TSB 19-103) before anything else.
2. Live-data B1S1 and B1S2 at warm idle. Healthy: S1 switching 0.1-0.9V; S2 flat at 0.6-0.8V. Failed cat: S2 mirrors S1.
3. B1S2 switching frequency at steady 40 mph: > 0.5/sec = cat done.
4. Inspect for exhaust leaks before the cat. Any pinhole upstream throws off mixture and false-triggers P0420.
5. On 1.5L turbo: check dipstick for fuel smell / elevated oil level. Oil dilution per TSB 17-091.
6. After 130k miles with everything else clean, the cat is almost certainly the cause. Use Honda OE or DENSO direct-fit only — generic universal cats rarely pass the Civic / CR-V catalyst monitor.

Possible Fixes

Can I Still Drive With P0420?

Yes — P0420 doesn’t affect driveability. You can drive the CR-V indefinitely with the code active. The two real-world consequences: failure of any required smog inspection, and slightly elevated emissions.

How Serious Is This Code?

Low. The 1.5L turbo thermostat case is worth doing quickly since the same fault hurts long-term engine wear from extended cold-running. The cat itself isn’t urgent unless you need to pass an inspection.

Repair Costs