press the gas pedal 5 times in 3 seconds after turning the car to run (not start). the check engine light will blink a sequence of numbers, designated by blinks.
it will go somethins like this:
and two more sets of numbers. Codes are read as 12xx. A 1221 is the o2 sensor. If it comes up other than 1221, come back with the code and I can tell you what it is.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>