Join Date: May 1999
Location: SE Florida, USA
The P1728 code can only set when in fourth gear. So if you turn off overdrive it will never set.
I can rule out the solenoid from here. The problem you have is common in those years. The apply piston for the torque converter lockup clutch has developed a crack. It leaks pressure which allows the clutch to slip. The PCM sees the slip and sets a code. The crack will leak more the hotter the trans gets as the fluid thins out. The only way to fix this is to replace the torque converter.
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Automatic Transmission Engineer 1988-2007
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