What causes P0420 on a Nissan Pathfinder?

Common causes of P0420 on Nissan Pathfinder: Downstream O2 sensor degradation on QR25DE Rogue or VQ35DE Pathfinder/Murano; Catalytic converter substrate deterioration on high-mileage VQ35DE V6 Pathfinder; Exhaust manifold gasket leak on VQ35DE causing inaccurate pre-cat O2 readings; Catalyst contamination from CVT fluid cooler leak (on models with integrated transmission cooler); Upstream O2 sensor contamination from oil consumption on QR25DE Rogue.

P0420

P0420 Nissan Pathfinder

Q: How much does it cost to fix P0420 on a Nissan Pathfinder?

Fixes for P0420 on Nissan Pathfinder include: Replace downstream O2 sensor with NTK or Denso OE and verify catalyst response, Replace bank 1 catalytic converter with Nissan OE or CARB-compliant unit on VQ35DE, Replace exhaust manifold gaskets and inspect manifold for warpage on VQ35DE, Inspect and repair CVT cooler leak; replace contaminated catalytic converter, Fix oil consumption on QR25DE, then replace contaminated O2 sensor and evaluate cat.

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 Nissan Pathfinder 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 Nissan Pathfinder.

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 Nissan Pathfinder.

Common Causes on Nissan Pathfinder

Downstream O2 sensor degradation on QR25DE Rogue or VQ35DE Pathfinder/Murano
Catalytic converter substrate deterioration on high-mileage VQ35DE V6 Pathfinder
Exhaust manifold gasket leak on VQ35DE causing inaccurate pre-cat O2 readings
Catalyst contamination from CVT fluid cooler leak (on models with integrated transmission cooler)
Upstream O2 sensor contamination from oil consumption on QR25DE Rogue

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 NTK or Denso OE and verify catalyst response

Replace bank 1 catalytic converter with Nissan OE or CARB-compliant unit on VQ35DE

Replace exhaust manifold gaskets and inspect manifold for warpage on VQ35DE

Inspect and repair CVT cooler leak; replace contaminated catalytic converter

Fix oil consumption on QR25DE, then replace contaminated O2 sensor and evaluate cat

Notes for Nissan Pathfinder

Nissan CVT issues can indirectly affect catalyst health through engine load and RPM patterns.

P0420 Nissan Pathfinder

What is P0420?

Common Causes on Nissan Pathfinder

Symptoms

Notes for Nissan Pathfinder

Check Nissan Pathfinder Specs