The MIL on my '13 Fit (77,600 mi.) went on and suddenly the auto trans wouldn't shift up and I couldn't exceed 30 MPH. Started up next day and the light was off and the car ran fine. Had engine air filter nad trans fluid changed and 4 days later the MIL went on and trans wouldn't shift up. Brought it back to mechanic but light was off ,car runs normally and he couldn't diagnose the problem because even after they drove it few times the MIL stayed off. WTF?

 

How big is your Mother In Law? (sorry..couldn't resist)
I'm not sure what you mean by MIL?

 

CEL
MIL is another way to say it, usually in varying areas.
Malfunction Indicator Light

 

Seems like you’ll need to get it to your mechanic, or someone that can check the MIL when it does it. It is weird that it wouldn’t store the code though, your mechanic did check for a saved code right?

 

Big enough to cause her own dedicated light to come on lol.

 

Trans fluid was changed days ago and now you have shifting problems. Check the trans fluid.

 

Was the correct type of fluid used in the transmission? If not then there is your problem. Best of luck, Clay