1990 Toyota Supra Base 6 Cyl 3.0L
can the check engine light come on by having the oil filler cap off when the car is running
171906 miles, today I drove 15 miles on the why into work this mornning and on the way back home the check engine came on I looked under the hood and the oil filler cap was missing because last night I added more oil becuase it has been leaking oil from the oil pan and a valve cover, The check engine light has never come on befor I have had the car for three years.
That could happened, the cap was opened, the oil fumes were getting into the air filter and the O2 sensor detected the excess fuel in the exhaust systems and it activated the light. Unplug the negative battery terminal for 20 minutes, it will clear the check engine light. I hope that will give you some ideas.