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You must have the sun to factory scan tool in order to read the transmission codes on this model. Please tell me what the exact numeric trouble code is that your mechanic retrieved. This way I will be able to give you some more specific advice. If you are replacing the transmission I would definitely go with either a rebuilt or a new transmission, the use transmission will save you some money but unfortunately you can't always be sure of the quality of what you're buying. You'll be investing a good deal of money and a rebuilt transmission will come with a good warranty