91 accord lx s light, Help!!
 

My grandfather just picked up a 91 accord lx with less than 120k. The s light comes on. The previous owners said they took it to a trany specialist and said there is no issues. I did some research and found that the wires get dirty and such and try cleaning them. My grandfather did so. Worked great no issue. Sat overnight issue came back. Double checked the wire cleaned them again Worked no issue. Overnight next day came back. unplug TCU issue gone. Overnight comes back. Dug deeper into the net today. told him to jump blue connector behind passenger kick panel then count flashes. What i read said count slight flashes. His car the engine light flashed 6 times.
So what am I looking for?
Is there 2 computers of just one here?
Thank you
P.S when the s light is not on car shift smooth and no issues. and if you press the sport button the light comes on witch i assume that is what its suppose to do.

Update
 

I did some more research on how to read the code on this car. According to my grandfather said the 6 engine light flashes are fist long then 5 short. meaning error code 15. looking that up I get defective ignition output signal. What that make the S light come on and affect the sifting?

My guess would be the TCU needs to get an engine rpm signal from the ECU to shift properly. On a Civic a code 15 is a serious internal ECU problem and usually the engine will not start.