P0420 RAM 1500
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 RAM 1500 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 RAM 1500.
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 RAM 1500.
Common Causes on RAM 1500
- Catalytic converter degradation from MDS-related oil consumption on 5.7L HEMI
- Downstream O2 sensor contamination from exhaust soot on 5.7L HEMI
- Exhaust manifold bolt failure causing pre-catalyst exhaust leak on HEMI V8
- Catalyst thermal damage from MDS-related misfires on deactivated cylinders
- Secondary catalytic converter underbody corrosion failure in salt-belt states
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 RAM 1500
Always resolve MDS-related misfires before replacing catalytic converters on HEMI engines.