I filled my tank up with 89 octane....could that cause my check engine light to come on?

 

no but the car will run like sh!t

 

Untrue.

 

In my experience, 89 miles, I had less milage then when I used 93 (I tested this during my drive down to Miami) and felt like it didn't give that much pick up (I could have imagine that tho but since the timing is retar....could be) your check engine light probably would not be caused by 89 octane unless you been using that for years and could get more carb build up

 

It might light up, then again it might not.

The computer will adjust the engine timing for the lower octane, and you might see a little bit of performance difference.

Why would you put in 89 in the first place?? Now you have to put 92+ in and let the computer adjust back to high octane fuel.