Mitsubishi Repair: service engine soon light, air passages, mishubishi

Question
I have a 2002 mishubishi galant sedan 4 cyl and i have replaced the o2 sensor in this car 3 times in the past year due to the service engine soon light coming on and it scanned a problem with the 02 sensor so we kept replacing it thinking the part might have been defective.  I had a mechanic do all this.  Well the service engine soon light came back on 2 weeks ago and i had it scanned same results.  my mechanic said it's not that it needs to be changed again it's something else.  He checked all the wiring and said he couldn't find anything wrong.  He told me to just drive it and see what happens and let him know.  well it comes on one day and then goes off the other.  I am soo puzzled.  any suggestions as to what it could be or if there is a known problem in galants with this.  any help would be great.  thanks.

Answer
Jennifer: It could be a problem with the computer, as it is what kicks on the light when it picks up a problem in the system. Could be the wires that hook to the 02 sensor is not hooked tight or as they should be. So the computer is picking something up and this code comes up. Still if the car is running ok, I guess I would let the light go for now. It could be the computer is for whatever the reason, thinks it picks up a problem when there isn't one. If you were having problems with that 02 sensor, your car would either run to rich or to lean. My repair manual says the computer is constantly monitors this variable voltage output to determine the ratio of the oxygen to fuel in the mixture. Oh hey while reading my manual, it says that when you replace the 02 sensor you should also check outside air supply, as the sensor is designed to allow air circulation to the internal portion of the sensor, so you are to make sure all the air passages are not restricted. So that could be the problem with your car, maybe the air passages are not all open as they should be. The manual says you are to be using unleaded fuel too. As that is essentail for proper operation of the sensor. It talks about the pigtail and electrical connector which is hooked to the sensor, so if some how that was damaged, the computer would pick up on that. Also if dirt, grease and other contaminants should be kept away from the electrical connector and the louvered end of the sensor and there is a silicone boot that must be installed in the correct position to prevent the boot from being melted and to allow the sensor to operate properly. I hope something in this will help you and good luck. Linda. PS: you could try (mitsubishisucks.com) and it will show you things about your galant.