I'm having an issue with my Honda and I have.

I'm having an issue with my Honda and I have tried doing research but can't seem to find the right answer.

I have a 92 Honda Accord EX.

The D4 Error Code is showing most of the time I am driving, and I can only shift to 1st and 2nd gear. Though, sometimes as of late the D4 Code might turn off and it will shift normally between the gears (though a little rough) or the D4 Code will flash, but it will still shift the normally. When I turn the car of though, it usually goes back to the same issue as I first stated. The previous owner of the car replaced the TCU about 8 months ago and said it was working fine up until about 2 months ago.

Could it be the TCU again, or is there another problem that could be going on and how would I fix it?