P0420 Ford Bronco Sport
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 Ford Bronco Sport 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 Ford Bronco Sport.
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 Ford Bronco Sport.
Common Causes on Ford Bronco Sport
- Close-coupled catalytic converter failure on 1.5L EcoBoost (Escape/Bronco Sport)
- Downstream O2 sensor failure from moisture buildup in short-trip driving patterns
- Coolant intrusion contaminating catalyst substrate on 1.5L EcoBoost (cracked head issue)
- Exhaust leak at turbo downpipe gasket causing inaccurate O2 sensor readings
- Catalyst efficiency loss from extended cold-start enrichment on three-cylinder 1.5L
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 Ford Bronco Sport
If the 1.5L EcoBoost has the cracked head issue, coolant contamination will destroy any new catalyst.