1990 accord ex f22a1 engine
when i drive 70mph or sometimes 55 mph on the freeway or highway the checkengine light comes on and when i start the car after i go into a store the check engine light doesnt show up so i cant scan it. does anyone have an idea what it can be? why it comes on while driving fast and it goes away after the ignition turns off

 

The check engine light will come on when the engine computer (ECU) detects the problem.

Even when the light is off, the computer saves the engine code, so you can still read it.

Short the service connector and count the flashes on the LED of the ECU.