is there a simple way to get the error code out of my 93 honda?

on my isuzu i could put a paper clip in it and make the dash blink a error code.

I just had a motor installed(used) and after driving around 20-30min i get a check engine light. Some have told me its most likely the o2 sensor. but they are like 69$ and without a job, I need to know what the real prollem is before i spend.