Service engine soon

I own a 1997 Maxima GLE. It has 104,875 miles it has been an awesome car. This past Friday the, "Service engine soon" light came on. I plan on taking it to the dealer to have it service. I am looking to get an idea of what the problem may be. I plan on having the car service for spark plugs (60,000 mile service) etc. I notice some other owner of 2000 Maxima GLEs' said that it was the Oxygen sensor. Thank you.

I have been having same problem. 00 Maxima GLE. Check engine light on, took it to a local shop (not dealer) they ran flow chart on it and checked codes. They said I needed all 3 O2 sensors. This was going to cost $700!! Called local Nissan dealers could get same service for $450.00. Took it to local dealer today, they ran codes and said it was not O2 sensors, they found the Mass Air Flow unit was bad. Cost for MAF unit and labor, $675.00. This sucks. They said it was due to someone used an aftermarket air filter. Bought car used at Ford dealership. I have not replaced the air filter since I bought it, 1 1/2 years ago.
Hope this helps.
If anyone else has heard about the aftermarket air filter, please reply.
Thanks.

I have a 00 Maxima SE with 80k. My check engine light came on and the engine is misfiring. I am very concerned because my sister-in-law was having the same problem, but didn't get it fixed before she had ruined her engine. After they replaced her block, they also put on a new ECM and Mass Airflow Unit. Those 2 parts alone are very expensive - is there any other alternative. (it's in the shop now - i am having new plugs put in, but I doubt it will help)