P0420 Chevrolet Malibu
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 Malibu 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 Malibu.
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 Malibu.
Common Causes on Chevrolet Malibu
- Close-coupled catalytic converter failure on 1.5L turbo Malibu from turbo heat cycling
- Downstream O2 sensor degradation from exhaust condensation in short-trip driving
- Turbo oil seal leak contaminating catalyst substrate with engine oil
- Exhaust manifold-integrated catalytic converter crack from thermal stress
- Rich running condition from PCV failure dumping excess fuel through catalyst
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 Chevrolet Malibu
The turbo-integrated catalytic converter on the 1.5T is expensive; verify diagnosis before replacing.