Q: My car shows trouble codes P0133 and P0420

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hello. I had my car serviced about 2 months ago the car's ob was throwing off a p133, p420 and p171.. I took it to the shop, the oxgen sensor was replaced. .I Drove the car for a couple of days and the ob was throwing off just p420, I was told that if i add catalytic converter cleaner to the fuel tank its going to clean the cataltic converter..so i bought the cleaner but a couple days later still get p420. Am thinking ok i might need a new catallytic converter, but since it's expensive i wait until a month later to try to have it replaced..before i have it replaced i check the ob with handheld scanner now am getting a p133 and p420. I should not be getting a p133 since i had the oxgen sensor replaced about a month ago. when i take the car back to the mechanic that replaced the oxgen sensor he tells me maybe i should replaced the catalytic converter first, that the p133 code might go away. i think he is jsut giving me the run-around..can u tell me what to do?? thanks

My car has 182000 miles.
My car has an automatic transmission.

Hi there:

It appears as if you’ve got a lot of miscommunication going on with your mechanic. Here are a few basics. First, anytime an error code is triggered, such as the P0133 OBD-II code the issue needs to be fixed and then the error codes need to be cleared with a professional digital diagnostic tool - not the basic hand held scanner being used. So, before you take it back to this mechanic to get more of a run around (which I agree you’re getting) contact a professional mechanic to complete a simple Check Engine Light inspection. This will allow them to pull all existing error codes, clear those codes and retest the system to determine what is wrong with your Corolla.

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