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Discussion Starter · #1 ·
My friend has a 1999 Taurus with the AX4N automatic. In cold weather, it shifts fine into overdrive, but when it gets warmer, it will only shift into OD when the engine is cold, and after it gets into operating temperature, it will refuse to shift into OD, unless you almost completely take your foot off the gas pedal, and then it will sometimes shift, but will immediately shift down again when you press the pedal down. I have tested all the solenoids with a 9V battery. All click fine and have the same resistance. I took off the valve body and examined the retaining clip (according to the TSB), which appears to be perfectly intact, and also checked the wiring connections, changed the fluid and filter, cleaned the cooler fins. All other gears and TC work fine. Does anybody here have any good info to check for?
 

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I know that it is a different trans, but on my '90 bronco with an E4OD I had a shifting problem due to a faulty VSS. The PCM uses the VSS to help to determine shift points. My problem was not temp related, and was in the opposite direction, it upshifted a little too soon, and I had to jump on it to get it to downshift out of OD.

I know that there is such a componenet called the turbine speed shaft sensor. I don't know what it does, but it sounds important, and electrical components have more resistance as they heat up.
 

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Do you have a Check Engine light on? or flashing? It should be scanned for codes even if the CEL is not lit to check for stored codes.
My experience with temperature related problems turned out to be internal leaks. The oil is thinner when hot, it leaks past o-rings/gaskets ect. Have you pressure tested it yet?
 

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Discussion Starter · #5 ·
I haven't pressure tested. I do have a trans pressure gauge somewhere. The CEL light didn't work before, but after hitting a speed bump one time, I think it is working now. I'll check the codes. Seems like I tried before and found nothing. I'm suspecting an electrical/electronic problem, because of many other electrical problems. I'm not sure where the VSS is, and if it is affected by trans or engine temp. I wonder if a broken spring (like an accumulator spring) could do it. I've changed the TPS and reseated the harness connectors (which made the A/C clutch work now).
 

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