What causes P0420 on a Honda Cr-V?

Common causes of P0420 on Honda Cr-V: Downstream O2 sensor failure on CR-V/Pilot/HR-V causing false P0420 reading; Catalytic converter degradation from oil consumption contamination on 1.5L turbo CR-V; Exhaust manifold crack or gasket leak on 3.5L V6 Pilot causing pre-cat exhaust loss; Catalyst efficiency loss from fuel dilution-related oil contamination on 1.5T CR-V (2017-2020); Upstream O2 sensor aging causing fuel control inaccuracy and catalyst overloading.

P0420

P0420 Honda Cr-V

Q: How much does it cost to fix P0420 on a Honda Cr-V?

Fixes for P0420 on Honda Cr-V include: Replace downstream O2 sensor with Denso OE and clear codes; retest after 200 miles, Address oil consumption issue first; replace catalytic converter with Honda OE unit if contaminated, Replace exhaust manifold gasket on 3.5L Pilot and inspect for manifold cracks, Apply Honda ECU update (TSB 18-074) to reduce fuel dilution and replace contaminated cat, Replace upstream O2 sensor and reset ECU fuel trim adaptation values.

Catalyst System Efficiency Below Threshold (Bank 1) · Powertrain Code · Medium · Repair: Moderate

What is P0420?

The catalytic converter on bank 1 is not operating efficiently. The downstream O2 sensor readings indicate the catalyst is not converting exhaust gases properly. May need catalyst replacement or could be caused by a failed O2 sensor.

When the Honda Cr-V triggers code P0420 (catalyst system efficiency below threshold (bank 1)), it typically points to an issue in the powertrain system. Below you'll find the most common causes, symptoms, and repair options specific to the Honda Cr-V.

This repair is rated moderate, meaning some experience and specialty tools required.

Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Honda Cr-V.

Common Causes on Honda Cr-V

Downstream O2 sensor failure on CR-V/Pilot/HR-V causing false P0420 reading
Catalytic converter degradation from oil consumption contamination on 1.5L turbo CR-V
Exhaust manifold crack or gasket leak on 3.5L V6 Pilot causing pre-cat exhaust loss
Catalyst efficiency loss from fuel dilution-related oil contamination on 1.5T CR-V (2017-2020)
Upstream O2 sensor aging causing fuel control inaccuracy and catalyst overloading

Symptoms

Check engine light illuminated steadily
Reduced fuel economy compared to normal
Sulfur or rotten egg smell from exhaust
Failed emissions inspection or smog test
Slight loss of power at highway speeds
Rough or uneven exhaust note

Recommended Fixes

Replace downstream O2 sensor with Denso OE and clear codes; retest after 200 miles

Address oil consumption issue first; replace catalytic converter with Honda OE unit if contaminated

Replace exhaust manifold gasket on 3.5L Pilot and inspect for manifold cracks

Apply Honda ECU update (TSB 18-074) to reduce fuel dilution and replace contaminated cat

Replace upstream O2 sensor and reset ECU fuel trim adaptation values

Notes for Honda Cr-V

The 2017-2020 CR-V 1.5T fuel dilution issue can contaminate the catalytic converter with oil.

P0420 Honda Cr-V

What is P0420?

Common Causes on Honda Cr-V

Symptoms

Notes for Honda Cr-V

Check Honda Cr-V Specs