What causes P0420 on a Kia Telluride?

Common causes of P0420 on Kia Telluride: Catalytic converter efficiency loss on 3.8L Lambda V6 (Palisade/Telluride) from age; Downstream O2 sensor slow response time on 3.8L V6 over 80k miles; Exhaust manifold gasket leak on 3.8L V6 from thermal expansion cycling; Catalyst precious metal depletion from high mileage and ethanol-blend fuel use; Upstream O2 sensor contamination from oil or coolant causing fuel control errors.

P0420

P0420 Kia Telluride

Q: How much does it cost to fix P0420 on a Kia Telluride?

Fixes for P0420 on Kia Telluride include: Replace catalytic converter with Hyundai/Kia OE unit on 3.8L V6, Replace downstream O2 sensor with OE Denso and clear codes before condemning catalyst, Replace exhaust manifold gasket set and inspect manifold for cracks, Replace catalytic converter with unit containing adequate precious metal loading for V6 volume, Replace upstream O2 sensor and check for oil or coolant leaks contaminating exhaust.

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 Kia Telluride 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 Kia Telluride.

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 Kia Telluride.

Common Causes on Kia Telluride

Catalytic converter efficiency loss on 3.8L Lambda V6 (Palisade/Telluride) from age
Downstream O2 sensor slow response time on 3.8L V6 over 80k miles
Exhaust manifold gasket leak on 3.8L V6 from thermal expansion cycling
Catalyst precious metal depletion from high mileage and ethanol-blend fuel use
Upstream O2 sensor contamination from oil or coolant causing fuel control errors

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 catalytic converter with Hyundai/Kia OE unit on 3.8L V6

Replace downstream O2 sensor with OE Denso and clear codes before condemning catalyst

Replace exhaust manifold gasket set and inspect manifold for cracks

Replace catalytic converter with unit containing adequate precious metal loading for V6 volume

Replace upstream O2 sensor and check for oil or coolant leaks contaminating exhaust

Notes for Kia Telluride

The Palisade/Telluride 3.8L V6 is generally reliable; P0420 is usually an O2 sensor issue first.

P0420 Kia Telluride

What is P0420?

Common Causes on Kia Telluride

Symptoms

Notes for Kia Telluride

Check Kia Telluride Specs