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My check engine light went OUT

The check engine went on on my 03 camry. The computer said it was the primary 02 sensor. another computer said it was the catalytic. The car has about 93000 miles.

I waited about 4 weeks trying to decide what to fix first. After filing the gas tank the light went out. I first thought the bulb burned out but it did not.

The gas milage is as good as ever. Could it be simply the winter formulation of gasoline made the difference? Any other ideas?


CEL don’t say it is an O? sensor or a converter. It is stated in code language like P1234. That gives hints as to a possible problem. From there it is back to the mechanic who can use that information to help him find the problem.

Many CEL's do go out after a while.  Some never come back.  If it does come back, then make sure you follow up on it. If it does not, then maybe it was a one time thing.  But if it does not go away, it is a very good idea to follow up why it is there.

I had a friend with an '01 Corolla. Her light did the same thing. I read the code, and it was P0420 for catalytic converter efficiency below threshold. After I told her what needed to be done to replace the cat, she decided to think about it. She called me a week later to say the light went out. It was a day or so after filling up. She did mention she used a different gas station than the last tankful. I told her no to use the previous station anymore. This lasted until just this year, 2 years later. The light would not go back out, and she needed to finally replace the cat to get the light to go out.

Maybe in a year or so, you will too.

Both computers probably “said” the same thing. As JE Meehan said the computer just spits out codes. And even those codes can’t say that parts are bad.

You do need to report the codes if you want informed advice. But lets guess, like maybe BustedKnuckles did, that the code was P0420.

This would make sense given what you have been told. What that code basically means is that the readings from the O2 sensor in front of the cat converter and the one behind the cat are too similar. If the cat is working well, they should be different.

So…this could mean that one of those sensors is bad…or that the cat is bad…or something else entirely that is messing with the make up of the exhaust (like maybe an exhaust leak or a tank or two of gas very high in some kind of contaminant).

Anyway, be happy and drive on. If the light should come back don’t let people guess about what to do. Find someone who will diagnose.