Well Dan, if I were guessing, I'd say it's broken .
Seriously, if this happened suddenly and there were no early warning signs, I'd look at the linkage first. I have seen this happen a number of times. Wouldn't it be nice if were something simple like that. If it isn't the external linkage, it could be internal linkage. If it's internal, best left to a tech. Good luck my friend.

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.