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P0420-1/1 CATALYTIC CONVERTER EFFICIENCY
Normally this means that the catalytic converter needs to be replaced
If the van has a lot of miles on it and recently had one of the o2 sensors replaced and not the other the engine controller may have been "tricked" into setting this code, any mileage over 70,000 and the sensors should be replaced in pairs, if one was replaced and not the other, have the other replaced and the engine controller reset, if the code reoccurs, check the following before replacement
The catalytic converter may have a factory extended emissions warranty on it if the van is less then 8 years old and has fewer than 80,000 miles on it
A few other things to check before replacing the catalytic converter, most of the time though when this code sets the catalytic converter will need to be replaced
Inspect the Catalytic Converter for the following damage. Damage Catalytic Converter, dent and holes. Severe discoloration caused by overheating the Catalytic Converter. Catalytic Converter broke internally. Leaking Catalytic Converter.
Start the engine. Inspect the exhaust for leak between the engine and the O2 sensor. Inspect the exhaust for leaks between the engine and the appropriate rear O2 Sensor.
Check the exhaust for excessive smoke caused by an internal problem in the engine. Repair as needed
I hope that this helps you
If you need more information just let me know