Car threw this code a couple of weeks back. At first intermittent, but eventually got to the point where it would cause the dash icon to come on without even driving. So just completed replacement of solenoids N88/N89, with filter change and replacement of fluid. A couple of notes for those who haven't done this and are thinking about the filter/fluid change.

1. Lot of info out there instructing to lower subframe to reach the corner bolt in the transmission pan. Bentley service manual instructs you to remove fuse box, driver side motor mount, and raise engine/trans to provide clearance for this. I followed the Bentley procedure, and it wasn't that difficult. The bolt is still hard to get to, as there just isn't much clearance, period. You can reinstall the torx head pan screw if you wish (size T30); I chose to replace with an allen head cap screw, which was easier to get started and tighten.

2. The fill procedure in the Bentley manual calls for filling through a plug in an almost impossible location. As near as I could tell, it's located near the passenger side output shaft (drive axle) on the housing. Manual calls for a special tool, 'shortened to 36mm', to remove the plug. Lot of information on the internet indicating people fill through another 'plug' on the top of the transmission, on the front near the oil filter housing. Frankly, that one is almost impossible to access as well. I used a 1/8" pipe thread nipple screwed in to the drain plug of the transmission pan, connected with flexible tubing to my pressure fill tank. Transmission was filled within 15 minutes. You will need to have the transmission fluid at the proper temp, and of course have the car running.

Hope this information helps a few folks out there!