300M engine warning light

Had my 300M oil changed by CTC.
After the engine warning light was steady on.
They said they didn't know why, but were able to turn it off with their
diagnostic equipment.
They said it would probably return, it hasn't yet over 1,500 miles of
driving over 3 weeks.
The operators manual says for an intermittent problem it should go out
after several starts. Only a flashing light is a serious problem.
I'm wondering what they could have done wrong doing an oil change; to
turn on the engine check light.

 

It would have been good if they had used their equipment to read the
code and tell you what it was reporting that was supposedly wrong.
Strange that they would not have done that.

Since you don't have that info., I'd forget about it, and if the code
comes back, then have it read (using the key dance or a code reader at
your local auto parts company) and act according to what it says.