Well, I'm not real sure what actually controls all this, but there is a method to the madness. I think!
There are output sensors on the transmission. These sensors take information from different components in the tranny and relay that info to the PCM. The PCM then either compiles that info or transmits it to the another compontent to output the info.
Ok... an example... How about an electric VSS.
The Vehicle Speed Sensor has a gear on the end that is spun by a gear on the output shaft of the transmission. The sensor counts the revs of the gear and transmits that information to the PCM. The PCM then translates that information and sends it to the Speedometer, which causes the needle to move around with the speed of the vehicle. At the sametime, it takes that same info, complies it and sends
that info - along with engine RPM info, to the shift solenoids which signals the proper shifting pressure and timing.
Since I'm not as familiar with OBD-I systems as I am with OBD-II systems, I'm not sure what measures engine RPM. Most likely the Crank Sensor, but still. If the CEL is not on and the engine seems to run fine, I would have to suspect either the PCM or the solenoid assembly on the tranny.
