Alright, so I have an annoying problem with an AW4 transmission. Since I know jack-squat about trannies, I was curious if anyone might be able to shed some light on it.
The trans works fine under most normal circumstances--city driving, short trips, etc. However, when it's out on the highway, after about 20-30 minutes it will lose the ability to shift itself. So, when it gets off the highway and into town, it's stuck in 4th and has to be manually shifted through it's gears. No up-shift, no down-shift, the only shifting it will do on its own is a full-throttle down-shift. But, after that, it will go right back to being stuck in it's original gear.
If I turn the car off and let it sit for a while, the trans will be back to working fine.
I was convinced it had to be tied to some sort of failure in the Transmisison Control Unit. For this particular trans, when the TCU dies it's designed so that in D it will always be in 4th, in 3 it will always be in 3rd, and in 1-2 it will always be in 1st.
However, the fact that I get no codes from the trans, and that it works fine until it's been on the highway for a while leads me to think that the TCU isn't really the problem. I'm guessing that in town the trans never reaches full temperature, and for some reason when it does on the highway and it gets to full temp, that's causing it to not shift. But, I have no idea why that would be.
I'm going to change the fluid when it gets warmer out, but if that doesn't work I'll be taking it to a shop. If anyone can give some insight as to why they think this would happen before I take it to a shop, it would be much appreciated.
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