1989 transmission and check engine light?

My civic has 1.5 ltr motor in it. Runs beautifully, i just flushed the transmission and with new fluid in it it shifts like a dream, unless i go over 80mph. Anytime i drive over 80 for an extended period the check engine light kicks on then it seems like it loses overdrive (or 4th gear) whichever. Anyone else had this similar problem? If i turn the car off and restart it, itll run great again until i go over 80.....

Umm, don't go over 80?

Ya, right. This car starts to handle descent around there. I wonder if the ecu could have anything to do with it.

well if the check engine light comes on, the *obvious* answer would be to check the ECU for the flashing light and get what code it is flashing.

some people......

well if the check engine light comes on, the *obvious* answer would be to check the ECU for the flashing light and get what code it is flashing.

some people......
:iceslolan