Rick's Free Auto Repair Advice

P0420 Catalyst System Efficiency

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

This code means the catalytic converter that treats the exhaust for Bank 1 has failed it’s testing. The oxygen sensor in front of the catalytic converter switches back and forth between rich and lean as the computer constantly changes air fuel mixture. But after the exhaust leaves the converter, the next oxygen sensor should not switch between rich and lean. If it does, that means the catalytic converter is NOT doing its job.

Catalytic converters generally do NOT fail on their own. They usually fail because of misfires that have not been repaired. That allows the engine to dump excess gas into the converter. The excess gas is burned off in the converter and causes internal core temperature to rise to the point of destroying the converter. All the precious metals melt. If you replace the catalytic converter but do NOT fix the underlying cause, you will be replacing the converter again and again.

Also, if you buy a cheap aftermarket converter, you are fooling yourself. Most of the cheap universal converters are missing Cerium, a metal that stores and releases oxygen. That will cause the converter to malfunction.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat


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