Failed emissions due to excessive Hydrocarbon (HC), Carbon Monoxide (CO) or Oxides of Nitrogen (NOX) are also frequently caused by a deteriorated catalytic converter. The problem is how to determine if the converter is really bad!
Converters consume oxygen in the catalytic process, which provides the basis for a simple, two minute 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 full open and instantly 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, emissions climb, the check engine light comes on and the computer stores a code. The oxygen capture test is quick, simple, and highly reliable and helps avoid buying an unnecessary and expensive converter. Always ask for an oxygen capture test before buying a replacement converter, it’s two minutes that could save you several hundred dollars.
