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2002 Rx300 Cel P0420 Help!


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Hello everyone, first of all my car has about 92k miles. While driving, the CEL light popped up and the VSC light also lit. I have an OBDII scanner and I check the code, the code is P0420 which is catalyst efficiency below threshold. I researched and some said that it could be the weather, gas, etc. So I removed the code and the CEL came back within 150 miles. Now I am stuck in a dilema. Can someone please direct me to what steps I should take now, what should I look for and what should I replace. I have also noticed that my gas mileage has decreased tremendously. Please someone help. Thanks and have a great night..


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I had a similar problem with our 03 RX300...CEL/VSC/Trac Off light on. Turned out to be a couple of things. Bad gas cap (replaced for $7 at Adv Auto) and the hose under the air filter box had come off and was making it read lean. The guy at AA checked the gas cap and it had gone bad and wouldn't click shut all the way. I read about the "air filter hose off" problem here of this forum. I also cleaned the Mass Air Flow sensor with MAFS spray.

Once I did this and had the codes cleared it has run fine with no lights on. Might not be what is causing your problems but they are a free/cheap check and fix. There are several threads about these problems on the forum...just use the serach function.

Good Luck

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Sounds like you have a bad 0xygen sensor ....Have you replaced it...by the way dont be confused with the ones up by the engine, they are air fuel sensors.... If you look under the car from the drivers seat area, you will see it. It has wires coming off it.

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