The Check engine light means an O2 sensor problem. Its a MYTH.
Anyone who has taken this to be true and has spent quite a bit of money on replacing oxygen sensors knows this is not true. First, you will not know, nor will anyone else, what the problem is until you have the trouble codes. Even if it is an oxygen sensor code, a lot of times there are other causes for the code to come about.
Vacuum leaks, poor fuel quality, low or high fuel pressure, a compression problem or a plugged catalytic converter could cause it. If the oxygen sensor is bad, then replacing the sensor still does not finish the repair. If an oxygen sensor failed, then there is a problem with the emissions of the engine. Usually when an oxygen sensor fails, it is because it has become contaminated. Contamination caused by an engine that is not running properly. So you will still need to determine where the originating problem came from. More often than not, there will be no trouble codes for that problem and it will not be evident without some specific tests.
