P0420 Chevrolet Tahoe
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 Tahoe 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 Tahoe.
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 Tahoe.
Common Causes on Chevrolet Tahoe
- Catalytic converter substrate deterioration from AFM oil consumption on 5.3L or 6.2L V8
- Downstream O2 sensor failure or contamination from engine oil fouling on bank 1
- Secondary air injection pump failure introducing moisture and damaging catalyst
- Exhaust manifold bolt failure causing pre-catalyst exhaust leak on 5.3L/6.2L
- Prolonged rich condition from failing fuel injector or fuel pressure regulator
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 Tahoe
Same AFM-related catalyst issues as GM_TRUCK_V8; full-size SUVs share the same powertrain.