I have a 1997 Honda Civic EX , sometimes engine light comes on but goes off again , I wonder cause they did work on exhaust , can it be a o2 censor gone bad?

My 1997 Honda Civic EX has a swap b16 with 5 speed transmission , every once in a wile the engine light comes on , but goes off again ...can it be a censor? Do they have the upstream  and  the downstream? For me its annoying to see a light in dash specially the engine light , if your going to sell the car and people see it they think something bad its wrong but this car its been like this for a long time , since where I live there is no inspection , I never bother to get it fix so when a person comes to see the car that wont scared them away.....lmao I hope someone can help me with this.... The car runs perfect no issues it has a b16 with 5 speed transmission , but that is the only thing that bothers me. I don't know if there is a code to turn it off , or one of the sensors are going bad , like I said it only comes on sometimes stays on for a wile then sometimes it goes off.....I don't know work was done on exhaust also so can it be that ?