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Hello and welcome to just answer and allowing me to assist you with your problem. sorry to hear about that dilemma , but before you start thinking of all things bad here is food for thought. All these newer cars with ECU that control everything from engine management to transmission operation need proper voltage and amperes to operate properly. If you know computers at all the phrase goes garbage in garbage out.So with that being said unfortunately it needs a good working alternator and battery so it can do it's job otherwise it will randomly pick it's own scenario causing a rash of weird things happening from engine issues to weird transmission actions. So before you jump to any conclusions of other problems do those two things first, replace the alternator and make sure the battery is good and charged. Hope this sheds some light on your problem and good luck. If you need any more assistance I would be happy to help.
Hello just checking in, if your happy with my answer please rate and reply so we may close off. If you need further assistance I'll be happy to do so.