What causes P0420 on a Chevrolet Traverse?

Common causes of P0420 on Chevrolet Traverse: Catalytic converter substrate degradation on high-mileage 3.6L V6 Traverse/Acadia; Downstream O2 sensor contamination from oil burning past valve seals on 3.6L; Exhaust manifold gasket leak causing false lean readings upstream of catalyst; Timing chain-related rich condition flooding catalyst with unburned fuel; Secondary cat (underbody) failure from road debris or salt corrosion damage.

P0420

P0420 Chevrolet Traverse

Q: How much does it cost to fix P0420 on a Chevrolet Traverse?

Fixes for P0420 on Chevrolet Traverse include: Replace bank 1 catalytic converter with OE GM or CARB-compliant unit, Replace downstream O2 sensor with AC Delco OE and clear fuel trim adaptations, Replace exhaust manifold gasket and inspect manifold for warpage, Repair timing chain issue first; replace converter only if efficiency remains low, Replace underbody secondary catalytic converter and inspect exhaust pipe for corrosion.

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 Chevrolet Traverse 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 Chevrolet Traverse.

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 Chevrolet Traverse.

Common Causes on Chevrolet Traverse

Catalytic converter substrate degradation on high-mileage 3.6L V6 Traverse/Acadia
Downstream O2 sensor contamination from oil burning past valve seals on 3.6L
Exhaust manifold gasket leak causing false lean readings upstream of catalyst
Timing chain-related rich condition flooding catalyst with unburned fuel
Secondary cat (underbody) failure from road debris or salt corrosion damage

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 bank 1 catalytic converter with OE GM or CARB-compliant unit

Replace downstream O2 sensor with AC Delco OE and clear fuel trim adaptations

Replace exhaust manifold gasket and inspect manifold for warpage

Repair timing chain issue first; replace converter only if efficiency remains low

Replace underbody secondary catalytic converter and inspect exhaust pipe for corrosion

Notes for Chevrolet Traverse

The 3.6L V6 has two catalytic converters per bank; ensure correct bank is diagnosed.

P0420 Chevrolet Traverse

What is P0420?

Common Causes on Chevrolet Traverse

Symptoms

Notes for Chevrolet Traverse

Check Chevrolet Traverse Specs