Help w/finding Engine Codes

I have a 1990 Lexus ES 250 and the check engine light comes on and off while driving :confused:. I heard that you can check engine codes with a paper clip and i was wondering if anyone knew more exact information on this. :dunno:
thanks in advance...

ok. so i figured out how to check the codes and the code was 52. the knock sensor. does anyone know where i can locate this sensor?

ok. so i figured out how to check the codes and the code was 52

deleted