How can i tell if my TCU is bad in my 1991 honda accord LX?

Question

when ever i put it in drive the S comes on even when i try to turn it off it dont work it still stays on and when im drivein you can feel it kick in to gears other then that the car drives good how could it tell? oh and the green light flashs at me to lol

Answer 1

The transmission warning light (blinking S light) comes on when the transmission control unit detects that the torque converter clutch in the transmission is not locking up.  that doesn't mean there is a problem with the torque converter clutch or with the transmission control unit.  Almost every case the reason the torque converter clutch isn't locking up is because the vehicle speed sensor that send a signal to the control unit stopped sending the signal.  when that happens, the transmission control unit doesn't know how fast the car is going so it won't signal the lock-up of the torque converter, hence it concludes there is a problem with the torque converter clutch circuit.

the vehicle speed sensor is the primary input for the transmission shifts,   without the signal from the VSS the transmission slams into gears because the shifts are going off a pre-determined shift schedule based on engine rpm and loading.

the VSS is located on top of the transmission.  its pretty easy to change.  I've found that the VSS is the problem in 99.5% of the cases on that year vehicle where the concern is the flashing S light.

hope that helps