Q: Transmission shifts randomly while in drive, no movement. What would be cause? on 2006 Chrysler Pacifica

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Speedometer surges 10-20 mph while in drive, foot on brake and no movement from vehicle. Speedometer reads 0 in park and acts normally when moving. There is a new whining sound noticed also coming around alternator area but may not be associated but coincidental new problem. Just purchased vehicle and got good report from mechanic during pre-purchase maintenance check 1 week ago. Fluid level checks good.
(1) Answer
Probably a bad speed sensor. They're generally cheap and easy to replace and nearly impossible to test when they're intermittent. I'd just replace it and see. I don't know on that specific car, but it's usually a wire connector and 1 or 2 screws and generally near the output shaft of the transmission above fluid level.