I have a 1999 Camry, which I love. My check engine light was on and the car wouldn't pass the emission test, I had it checked out and the 1st Oxygen sensor was bad. I replaced it, reset the computer, and it was great! The light went off, and my car passed. This lasted for about 6 hours, then the check engine light came back on. I took it back to the same place, had it tested again. The same code came up, so I thought I got a bad part. I replaced the part again, the light went off, and I thought I was good again. This time it only took about 30 minutes for it to come back on again. I have searched for the answer to this, but does anyone know what would be causing the O2 sensor to go out over and over again? There is no other codes coming up during diagnosis.
This is a difficult problem to detect because the computer can not sense a malfunction, the vehicles computer system thinks everything is ok. In reality what is happening is the electrical component inside the MAF sensor becomes contaminated by air impurities. These containments imbed themselves to the electrical component that senses the air flow causing the sensor to be slightly off, but not enough to trigger the MIL (malfunction indicator lamp). Replace the MAF sensor with a new. NOTE: (Mass Air Flow MAF sensor or Air Intake Sensor AIS, depending on manufacturer. It does the same thing only with different names).