Engine code P1815

My '03 Malibu is running rough. I hooked up a scan tool and pulled up two codes: P1815 and P0300. I found out P0300 is a cylinder misfire. I also found out P1815 has something to do with the transmission. If someone out there knows exactly what P1815 means and what might cause this code to come up please let me know. My car has 38,000 miles on it and is past the 36,000 mile warranty. My owner's manual states some parts are covered for more miles since I live in California so I am trying to build a case to convince the dealer to pay for this repair. Please help with any suggestions.

When the Engine Controller detects a gear range other than PARK/NEUTRAL indicated at start-up, DTC P1815 sets.

There is a TSB #03-07-30-021A on complaints associated with this code but not sure if applicable to your vehicle