Staying in second gear is called "limp mode" that allows you to drive slowly to a repair shop without needing a tow truck.
In general, when it starts out in second gear without going through an up-shift, it's usually a speed sensor or other electrical problem. When it doesn't go back to second gear until or during an up-shift, that is usually caused by slippage of a clutch pack and will lead to the need to a rebuild.
There WILL be at least one diagnostic fault code stored in the Transmission Computer. An experienced transmission mechanic will know how to proceed after reading those codes.
Tuesday, August 7th, 2012 AT 9:22 PM