My '91 Accord is having problems with the "S" (sport) light remaining on. Having done immense research on this, I have discovered if the TCU (Transmission Control Unit) is replaced the issue will resolve itself. According to the research the TCU capacitors fail and cause errors to the transmission making it run in "limp mode". I can manually shift gears from 2 & drive which work but overdrive (4th gear) and 1st don't work at all.

So if the TCU is replaced will this solve the problem or is there more to it?

Thanks

 

Are there any codes stored in the TCU?
Two wire blue connector above the passenger kick panel.
Jumper it with a wire.
Turn ignition to II(ON) and watch the S or D4 light for blinking.
Record codes.
Report back here.

 

Done that and nothing came up. No blinking.

 

Have you cleared the memory by pulling the fuse?
If the transmission shifts fine after wards then it may be a sensor issue and the TCU may set a code proper rather than just going into limp mode.

 

Which fuse needs to be pulled?

 

ECM Memory fuse, underhood. If you have a radio that has a security code, make sure to have the code before wiping the memory.

 

https://honda-tech.com/honda-accord-.../#post38686391

Okay so after pulling the ECM fuses (24 & 28) nothing else happened. Still the same!

Noticed fuse 24 is a 10 amp rather than 7.5? Don't suppose that makes any difference?

 

Pull the #24 fuse, replace it with a 7.5A fuse. That is for the memory.
#28 is for the Main Relay. It will not affect memory.
If installation of the 7.5A fuse causes it to fail then check where the high current draw is coming from.
Verify the 10A fuse you pulled is still electrically good.