Hey any help appreciated.
I have a '97 Accord SE completely stock. I've been doing some routine maintenance on it recently and just an hour ago I started getting a CEL 41 code which I found is the primary o2 sensor heater after searching here. I don't know if that code is 100% correct cause it seems like an OBD-I code and the car is OBD-II right? But it's 4x 1sec flashes then 1x 1/2 sec flash. Earlier today I drained and filled the coolant then changed the automatic transmission fluid. The car ran just like before with no CEL for hours and now all of a sudden there's a CEL and I don't know if I did something wrong or it's just coincidence it decides to throw a CEL when I do some work on it.

Basically, what should I do next? Replace the o2 sensor and see if it still throws a CEL?

 

So, I just found oil in the spark plug cylinders...

Could oil be leaking into the cylinders/combustion chamber and this is whats causing the o2 sensors on the exhaust to trigger a CEL?