1999 Pontiac Grand Am • 115,000 miles

My mom was driving it earlier today and said there was a problem with the shifter. She said that when she put it in drive, it wouldnt drive. She tried multiple times to put it in drive and back to park until it went. I drove it after her and it worked fine, what is the problem and the cost of it to repair?
December 18, 2012.

It might just be the shifter interlock not allowing it to go into gear all the way. Otherwise I think there might be something loose in the shifter linkage at the shifter or at the transmission.
I am attaching some diagnostic information as well as the wiring diagram. The solenoid for the system may be intermitantly failing.
It is hard to estimate the price as I don't know how hard it is to get to solenoid. I would suspect 4 hours of labor, rate depends on shop, if labor is $75 that would be $300.00 in labor and a solenoid migh be $80.00 at the most.