P0420 Kia Sorento
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 Sorento 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 Sorento.
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 Sorento.
Common Causes on Kia Sorento
- Catalytic converter failure linked to Theta II engine issues on Tucson/Sportage/Santa Fe/Sorento
- Downstream O2 sensor failure on 2.5L Smartstream causing false P0420 code
- Exhaust leak at turbo downpipe gasket on 1.6T or 2.0T GDI models
- Catalyst contamination from excessive oil consumption on Theta II 2.4L GDI engines
- Aftermarket catalytic converter with insufficient precious metal loading failing prematurely
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
Notes for Kia Sorento
Many P0420 issues on Hyundai/Kia SUVs are secondary to Theta II engine problems; fix engine first.