Cadillac Repair: Trouble code, oxygen sensor, service engine soon light

Question
I have a 1994 Sedan DeVille with the 4.9 litre engine.  After driving for a while the 'service engine soon' light would come on.  I checked the trouble codes and it gave me a history codes of P012, P013, P052 and P070.  I cleared the codes.  THe next time I drove the car the light came on again after driving for a little while.  When I checked the codes it only gave P013 HISTORY.  What can I do to fix the problem and make the light stop coming on?

Answer
Sounds like an intermittent working rear oxygen sensor.

Clear the P013 code again and see if it returns. If it does, replace the REAR oxygen sensor which is just in front of the catalytic converter.

Then CLEAR the code and drive the car and see what codes come back as HISTORY or cURRENT.