I am recently advised that my 1992 Honda Civic EXV, 4-door sedan, 4-cyl 1600cc SOHC VTEC engine, automatic transmission DOES NOT have a separate Transmission Control Unit (TCU) / Module (TCM).

Looking at the wiring diagram for the Engine Control Unit (ECU) / Module (ECM) I see that it connects externally to the Interlock Control Unit A/T and Shift Position Module A/T.

Does the ECU control the entire operation of the A/T or does it just control the Shift Interlock?

If the entire operation of the A/T why then does the car run with an ECU intended only for a standard / manual transmission?

I see that there no suggestions as to how the ECU for a standard transmission is able to control the automatic transmission.

The engine works fine, the gearbox works fine but the Shift Lock mechanism is disabled. The ECU for M/T has none of the electronic components that ouput to the Shift Lock Controler and Shift Lock solenoid like the ECU for A/T.

This is easy to understand.

What I don't understand is that if the ECU in the A/T fully controls the entire operation of the A/T, then how can the ECU for a M/T be doing the same thing?