Just joined to let everyone know how I finally fixed my 2010 Highlander 2-3 shift flare (U151F transmission). I didn't see anything in these forums that matched my experience, so forgive me if it exists somewhere.
My 2010 Highlander started flaring from 2-3 shortly after I bought it used (@ 104k miles). I went through multiple remanned valve bodies, solenoids, and drain/fills to no avail. What finally fixed my 2-3 flare was a replacement of the transmission wiring harness. It cost me about $60 and took about 2 hours. You do not need to remove the valve body, just drop the pan and unplug the solenoids. You'll then need to man-handle the harness out of the top of the transmission. I had to use vice grips and broke the connector when pulling. It was in there tight. When I put the new one back in, I coated the o-ring in transmission fluid and needed to GENTLY tap the connector in place with a long screwdriver and a rubber mallet, going slowly around it to tap it in evenly. It eventually snapped in place. Once I replaced the harness, the flare still existed (was MUCH better, though) but was getting better over a few days of driving. I assumed that after 22k miles of trying to compensate for a intermittenly bad wire, it needed to re-learn how to shift properly. I had Toyota reset the transmission shift data and it went away completely. Cost me $197 for them to do that.
I have no long term data as I traded the Highlander in for a minivan once I fixed it, but as this was the first time I got the flare to go away completely in 3.5 years (~22k miles), I was confident it was finally fixed. After all those issues, I unfortunately lost confidence in Toyota's mighty reliability claims. I still own a very reliable Corolla, though.
For what it's worth, when I called the Toyota dealer to order the transmission wiring harness, they said that all the dealers in my region of my state had that exact part on backorder, with a minimum of 6 weeks for delivery. I assume this must be a common failure part. Might be worth changing if you have the 2-3 flare that won't go away.
I hope this helps someone.
My 2010 Highlander started flaring from 2-3 shortly after I bought it used (@ 104k miles). I went through multiple remanned valve bodies, solenoids, and drain/fills to no avail. What finally fixed my 2-3 flare was a replacement of the transmission wiring harness. It cost me about $60 and took about 2 hours. You do not need to remove the valve body, just drop the pan and unplug the solenoids. You'll then need to man-handle the harness out of the top of the transmission. I had to use vice grips and broke the connector when pulling. It was in there tight. When I put the new one back in, I coated the o-ring in transmission fluid and needed to GENTLY tap the connector in place with a long screwdriver and a rubber mallet, going slowly around it to tap it in evenly. It eventually snapped in place. Once I replaced the harness, the flare still existed (was MUCH better, though) but was getting better over a few days of driving. I assumed that after 22k miles of trying to compensate for a intermittenly bad wire, it needed to re-learn how to shift properly. I had Toyota reset the transmission shift data and it went away completely. Cost me $197 for them to do that.
I have no long term data as I traded the Highlander in for a minivan once I fixed it, but as this was the first time I got the flare to go away completely in 3.5 years (~22k miles), I was confident it was finally fixed. After all those issues, I unfortunately lost confidence in Toyota's mighty reliability claims. I still own a very reliable Corolla, though.
For what it's worth, when I called the Toyota dealer to order the transmission wiring harness, they said that all the dealers in my region of my state had that exact part on backorder, with a minimum of 6 weeks for delivery. I assume this must be a common failure part. Might be worth changing if you have the 2-3 flare that won't go away.
I hope this helps someone.
