Chevrolet Repair: P0749 code....AHHH, just hit 100K...., acura cl, shift problem

Question
99 Acura CL 3.0, just hit 100k today. Then my check engine light came on, had it read by a nearby mechanic. P0749.
He said it was external. (reminder:I know very little of Transmission) Can I just by the part from Acura? What should I do....the car is not moving from 1st gear!Do I need to just by a rebuilt trans? I was hopeing to just replace the 1 sensor.....
I am ready to buy a new car, however Acura will only give me $2k for the car. I would like to do a quick or cheap fix to feel comfortable to sell it, get $5k if possible.
Any suggestions????

Answer
Hi jennifer ... i haven't done much work on Acura's but if it is a trans shift problem, first check fluid level and smell it ...does it smell burnt... if not it could be a shift relay gone down...look around for a trans guy not the dealer as they will just try to get you into a new one and yours may just be a simple fix. i know that on some of those cars that if relay goes or trans computer they default to 1st gear... hope this helps...merry christmas