Catalytic Converter Efficiency Calculator

Calculate three-way catalytic converter conversion efficiency by comparing upstream and downstream emissions readings.

Input Parameters

Results

--
HC Conversion Eff
%
--
CO Conversion Eff
%
--
Catalyst Health
--
Light-Off Status
Note: OBD-II monitors catalyst efficiency via rear O2 sensor switching rate. A healthy cat converts 95%+ of HC, CO, and NOx at operating temperature.

Reference

HC Efficiency = (1 - Downstream_HC / Upstream_HC) x 100 CO Efficiency = (1 - Downstream_CO / Upstream_CO) x 100 New cat: >95% efficiency, Failed: <70% Light-off temperature: ~400-600°F Three-way cats also reduce NOx at stoich