P0420 Dodge Hornet
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 Dodge Hornet 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 Dodge Hornet.
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 Dodge Hornet.
Common Causes on Dodge Hornet
- Close-coupled catalytic converter failure on 2.0L GME turbo from turbo heat cycling
- Downstream O2 sensor degradation from exhaust condensation in the turbo exhaust system
- Turbo downpipe gasket leak causing pre-catalyst exhaust dilution
- Catalyst contamination from turbo oil seal seepage on 2.0L GME engine
- Rich running condition from MultiAir system errors overloading catalyst with unburned fuel
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 Dodge Hornet
The Hornet 2.0L turbo cat is close-coupled and subject to extreme heat from turbo exhaust.