Hi all, new guy here. anyways, trying to get my 91 lx back up to snuff. trying to fix the check engine codes. i'm getting a 1, 15 and 41. i have plans to replace the o2 sensor to clear he 1 and possibly the 41 but have no clue what the 15(Ignition Output Signal) could be. any ideas, common causes?

also, i'm trying the fix a small oil leak i have. i was told by the guy that did my tranny that it was coming from the oil sending unit close to the filter(he thought it was the filter till farther inspection). any ideas on that one? i will probly going to take it in for that one but don't wanna get screwed(i have minimal car knowledge).