My check engine light has been going on and off since march. i went to get an inspection and it went on... but I was early so I waited. the light went off and i got my emissions/inspections stickers, everything passed. Since then, my check engine light has been going on and off for about 3 weeks at a time. I've checked twice and its P0420 - Catalyst System Efficiency Below Threshold. I'm hesitant to replace my catalytic converter since the code keeps going on/off, i'm thinking maybe an O2 sensor is bad? Plus OEM CatCons are so damn expensive. Has anyone had this issue or know what could be causing the light to go on and off. I would imagine if the catcon was really bad, the light would stay on and not go off.

also, this is probably not an issue, but looking under the car there is a piece of clear plastic (like a plastic bag, but it's much thicker than a standard plastic bag) that is stuck to the catcon. It has been melted to it and is hanging a bit, I tore off what I could... Not sure how it got there...

 

Toyota has a service bulletin on this code, see link below:

http://townhall-talk.edmunds.com/direct/view/.f16db86

This could be the problem. Your car may no longer be covered by the warranty.

Any exhaust leaks or connection between the engine coolant temp and the light being on.

Might also be a bad 02 sensor but without some diagnostic work and a specific 02 code you would be guessing. Seldom does this code appear without a converter problem (or the issue covered by the Toyota bulletin.

The dealer or a shop with an ODBII diagnostic tool should be able to determine if the 02 sensors are working OK by viewing the sensor signal pattern.

There is no direct method of indicating the converter is bad. There are 02 sensors before the converter and one after it. The signals of the sensors before the converter are compared to the signal of the sensor after the computer. If the converter is working the rear sensor will have a certain pattern. If the sensor does not have have this pattern the code will be set.

The computer will preform a diagnostic check only when the coolant temp is stabilized, engine warmed up. And the engine is within a certain RPM range for a certain period of time. Thus if the code is cleared (or goes away on its own) it may take a while for it to come back.

If you need an OEM converter and can do the job yourself try the site below for discount Toyota OEM parts.

www.1sttoyotaparts.com

877-810-7067

If calling identify yourself as an internet customer to get the discount price.

 

my car misfiring and check engine light is on with codes reading P0351,P0352,P0352,P0353.

 

Year and engine type?