My van is 3.8 engine with overdrive automatic,and it started downshifting late after stop with a hard bump. It feels like someone tapped the back bumper when it sellects low gear wether your in overdrive or 3. I had an Actron diag. code reader hooked up at Autozone which said the transaxle control module has malfunctioned and theinput speed sensor 1 circuit malfunctioned with explanation ECM has detected that the input speed signal changed suddenly. I don't know if I should change the sensor or where it is located on transaxle.

 

OK, first autozone is totally useless when it comes to diagnosing trannies.

You MUST use a scanner with data stream capabilities.

However is your transmission shifting normally up and down except for comming to a stop? if so, your problem is an internal issue knows a bump stop. it is related to the Low/Reverse piston.