This is for my W124, 300E - check engine light has always been on, with engine running. I'm guessing it is the O2 sensor, saving that project for another day.
However, the last few fays, the light STAYS ON even after I shut off the engine and TAKE THE KEY OUT
I replaced the overload protection relay in October of last year. Could it be defective already?
Or is the car possessed by some menehunes playing tricks on me?