This response is directed to two seperate posts, with the same question subject. The "computer" gets signals and readings from the transmission as well as the engine.
According to the information I found in my Chiltons, and Haynes manuals. 1984-1995 Caravan/Voyager/Town & Country
1. The Single Board Engine Controller (SBEC), also referred to as a Powertrain Control Module (PCM), is located behind the battery.
2. The SMEC, SBEC, SBEC II, or PCM, are designed to test their own input and output circuits, if a fault is found in a major system, this information is stored in the SMEC, SBEC, SBEC II, or PCM for eventual display to the technician by means of the instrument panel CHECK ENGINE or by connecting a diagnostic readout tester and reading the numbered display code, which directly relates to a general fault.
3. To enter self diagnostics, start the vehicle and cycle the transaxle selector, and A/C switch if applicable. Then shut off the engine. Next in rapid succession turn the key switch ON, OFF, ON, OFF, ON and read the CHECK ENGINE flashes to interpret the fault codes stored in the SMEC, SBEC, SBEC II, or PCM.
4. The SMEC, SBEC, SBEC II, or PCM only stores fault codes for a period of between 50 and 100 iginition key ON/OFF cycles.
5. If the battery is disconnected for a short period of time, and the same procedure is followed as reading the codes, turn the ignition key to the on position, cycle the transaxle selector, and A/C switch if applicable. Then shut off the ignition key switch, and reconnect the battery, the SMEC, SBEC, SBEC II, or PCM will then go into a learning mode starting with the basic parameters which it was given upon manufacture.
There aren't too many codes listed in my manuals pertaining to the transmission, but enough to not spend the time to list them all in this thread.