There is little info online regarding the replacement of this part for the 4T80E transmission. My grandma's 2005 Cadillac DeVille PRNDL display randomly stopped moving from park and it would only stay parked or go into neutral. It ran perfectly fine until one day it stopped working. A regular shop said the transmission was toast (... always get a second opinion). The dealership said it was the internal mode switch, aka this. The stupid plastic clip broke but I replaced this entire thing anyway. What I didn't know was that you need the alignment tool to put on the lower valve body when installing for it to actually work, so now I've got to drain the fluid and tear it apart again. The alignment tool part number is DT47707-1 or J43708-1- definitely buy it on eBay for $20-30. Another tip: take pictures of where all the bolts go into the valve body as they have to be nearly flush otherwise it'll hit the transmission pan and won't seal properly and leak fluid all over - ask me how I know. Good luckEDIT: even the alignment tool didn't make a difference. The issue prior to using the alignment tool was it was stuck in 1st and 2nd gear and wouldn't move. Prior to doing any work to the car, it would start but PRNDL would stay in park or go into neutral, now it won't move from 1st but maybe neutral (not sure since I haven't taken it off jackstands...). The alignment tool is an overglorified spacer and totally unnecessary.. there are three bolts holes that align where the internal mode switch can be. Don't buy it. It's a cash grab. Anyways... now to figure out how to get this thing to start since it won't because it thinks it is in 1st gear.