Just had oil changed on my 1997 S 320 by.

The light means the Engine Computer detected a problem that could adversely affect emissions. A diagnostic fault code has been stored in that computer. The place to start is by having the code read. That will indicate the circuit or system that needs further diagnosis.

The Check Engine light has never come on yet in my '88 Grand Caravan either except when I caused it by unplugging a sensor. That doesn't mean the computer won't detect a problem tomorrow. It's doubtful your light is related to the oil change but to be safe, check the oil level before driving further.