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Vehicle is a 2003 Neon with 2.0 L 4 cylinder engine and 4 speed automatic, 40TE transaxle. Engine has 207,000 miles and transmission has about 100,000 miles since last rebuild.

I removed the transmission / transaxle pan, l drained fluid, replaced filter with Wix brand. I added about 5 quarts of ATF+4 fluid purchased from Advance Auto. I also flushed 4 additional quarts of fluid through the radiator transmission cooler. Fluid is at the proper level on the dipstick. It is half way between the add and full mark for fluid at operating temperature.

Now after this transmission service the vehicle exhibits what I believe is called bump shift. When slowing to a stop from 40 mph or greater and when the vehicle reaches about 25 mph there is a noticeable bump or jerk or some harsh downshift in the drive train. This behavior was NOT present before the fluid and filter change. Can a fluid and filter change cause a harsh downshift? If this shifting behavior is caused by the fluid, that would mean that there are some slight differences in the formulation of ATF+4 among different vendors or Advance Auto is fudging on the formulation it is using??? Has anyone else experienced such behavior after a fluid and filter change on the Chrysler 4X TE transaxles? Do I need to do another fluid flush with a different vendors ATF+4 fluid???
 

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That may be a 4-3 downshift bump that was addressed in TSB # 21-006-03. It involves a TCM reprogramming.
http://www.ertyu.org/steven_nikkel/neontsbs/2003/21-006-03.pdf
Shift behavior can change after a fluid/filter service due to slightly different viscosity and fresh fluid characteristics. A quicklearn may solve it, but having the newest software is recommended (if you don't already have it).
http://www.amsoil.com/techservicesbulletin/drivetrain/tsb%20dt-2008-10-02%20erratic%20shifting.pdf
 

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Discussion Starter #3
Since the transmission control software is adaptive and learns, will the software adapt within normal driving and this bump shift improve / disappear after a few hundred miles of driving? Will continued driving with this situation enhance wear and shorten transmission component life? I am really chapped that changing fluid causes problems within the software control.
 

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Discussion Starter #4
Update on the harsh downshift occurring around 25 mph.

In the last 6 weeks and after driving the vehicle 2800 miles, the harsh downshift as the vehicle de-accelerates through 25 mph has disappeared. I believe the transmission controller software corrected this condition and softened the downshifts. It adapted or relearned its procedure for applying the clutch for downshifting. Now it is barely noticeable and that was the situation before the transmission fluid change.

I am glad it fixed itself but it does seem bizarre that a fluid change would cause this problem in the first place. At least I did not have to pay a whopping fee to a dealership service department for a procedure that may or may NOT have worked.
 
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