Hyundai Repair: 1997 Elantra, hyundai elantra, numerical digits

Question
Purchased a 97 Hyundai elantra and replaced the o2 sensor.  the check engine light went out but then came back on a day later. i detached the battery and reattached and the check engine light went out.  i drove about 80 miles and the light is back on. any suggestions?

Answer
There are many, many potential problems that can cause a check engine lamp to come on.  Even after clearing the lamp, it will come back on again if the engine control module (ECM) sees a problem again.

To help you repair this, I'll need to know the diagnostic trouble code stored in the ECM.  It will be a five digit code of the form Pxxxx, where the x's represent numerical digits.  This will let me know what type of problem the ECM saw and enable me to advise you on how to locate and repair the cause of the problem.  AutoZone and AAMCO have advertised they'll read you trouble codes for free.