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?

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1991 300E 124.030 103.983KE 722358 03 412178
207K

1979 240D 123.123 250K (Project car)

2000 Ford Ranger, 187K

2015 Dodge Ram 1500 EcoDiesel 37K