420 code with a check engine light - 2005 Buick LaCrosse

The second sensor for the catalytic efficiency just looks at what's coming through. If there were no codes for an oxygen sensor then the catalyst may be going. Not unheard of. If it's going bad the code will start coming back more frequent.

Amy, P0420 Catalytic Converter Efficiency Below Threshold.

get it checked by code reader when they flash shouldnt drive it may cause more damage

I couldn't find engine code for 420 but may be body code take to AutoZone for free test and code meaning

Did you change catalytic converter or is leak in exhaust.

www.engine-light-help.com/generic-check-engine-light-codes.html

You Prabably need a new catalytic converter. Very common problem with toyotas. You will need to get a dealer part as the aftermarket converters will put your check engine light on eventually.

if the code is p0420
it means
catalyst system efficiency below threshold
(cylinder bank no.1)

You could have an enefficient converter. Question is what caused it to go bad? I have attended seminars on code 420, Possible causes are lack of spark or clogged fuel injectors. there have been times where the spark plug wire lays on the engine and over time it wears a weak spot in the side of the wire, its not enough to throw a miss fire code but it keeps the full amount of spark from getting to the plug and not burning the all the fuel in the cyl. A leaky injector would also cause to much fuel to be deliverd into the cyl and not get burned.

Hope this helps.

Code 420 is a catalytic converter is not working properly.Check the converter for leaks and the rear oxygen sensor for leaks.If they are good then you should replace the converter and clear the code.Good luck.Good luck.