As much as there may be 200 or whatever different auto transmissions on the road, they all operate by the same basic principles with the same basic kinds of parts. The details vary and those can be pulled from a shop manual.
I assume the code is P0730 (these codes have only 4 digits). That is frequently taken to be the kiss of death as it basically means the transmission is slipping. (Its normally generated by output shaft speed that is wrong given input shaft speed - i.e. the transmission isn’t putting out the revs the engine is giving it). However, this can have more than one cause. Many of those causes mean that you need a new transmission (dead internal clutches, seals…). Some don’t (e.g. solenoids that don’t provide proper pressure). So you have a code - but you still need an actual diagnosis. Given the history of these transmissions I’ll give you about 90/10 odds that you’ll need a new trans if you want to keep the van.