Volvo Repair: Volvo 1990 740, waranty, junk car

Question
QUESTION: I recently had the transmission rebuilt for my sons can 1990 740.  It ran fine for about 6 months and now it will not shift out of 1st gear.  I brought it back to the tranny shop and the tranny is under waranty but the tell me that it is the ECM not the transmission.   Does this make sense? Additionally I can buy a module on ebay or a junk yard a lot cheaper than they want to charge me, are thes modules plug and play or do they require re-programing.  If this doesn't work I'm afraid the car is headed to the junk yard.  Thanks in advance.

ANSWER: Not sure I understand...that transmission isn't controlled by a ECM

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QUESTION: I think you answered my question.  I don't think they want to rebuild the transmission so they gave me this story about the ECM.  What else coould possible cause the car not to shift.  If the car is in drive when it is ready to shift it disengages and you get nothing.  If I put the car in first it stays engaged.

Answer
Check the fluid level, first,check the color and odor to detect any burning. I suppose it is possible to screw up the linkage, awfully hard to make it do what your car is doing if possible at all! I would contend that there is an internal transmission problem.I didn't do alot of transmission rebuilds, we replaced the unit with either a good used one from a junk car or purchased a rebuilt unit. There are alot of poorly rebuilt units around, I don't trust . I would find a junkyard that would warranty the trans for at least 30 days and go with that.