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Q: Auto Trans will not shift by itself. on 1990 Toyota Supra

The car is an '87 non turbo automatic. you have to shift the trans manually. I changed the transmission and the problem is the same.
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Sounds like you should check the tranny ecu located behind the passenger foot well. There's a large harness there. Under normal working conditions, unplugging this will cause you to have to shift manually. Perhaps, if you're lucky, it's simply unplugged. Otherwise, you may have to change the ecu. You can pick one up form the junkyard if that's the case. The A340 trans came in a few cars, most notably the MKIII Supra and Cressida.
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