My car failed emissions test. My mechanic says it could be the catalytic converter, and there is no reliable way to test the catalytic converter. Is this so?No! Converters consume oxygen in the catalytic process, which provides the basis for a simple (the test only takes a couple minutes) converter efficiency check referred to as an oxygen capture test. Using an exhaust gas analyzer the percentage of oxygen coming from the tailpipe of a fully warmed-up vehicle is measured at idle. Once the oxygen reading has stabilized the throttle is rapidly snapped open (full throttle) and then closed. Following the throttle snap there should be a slight increase in the amount of oxygen coming from the tailpipe. The allowable “slight increase” is typically 1.2%. If the oxygen increase exceeds the allowable limit the converter is almost always bad.
In a healthy converter the catalytic reaction consumes large quantities of oxygen. Therefore an excessive increase in oxygen at the tailpipe, following the snap test, indicates the converter has lost its ability to capture and use oxygen. Without capturing and consuming oxygen the catalytic reaction stalls and emissions climb. The oxygen capture test is quick, simple, and highly reliable.
