What is the part number for this item on a 2005 Infiniti g35x sedan? Manual mode seems to work only on initial startup . After shutoff, the drive mode is only available even when the selector is in the manual mode position. After sitting for awhile, manual mode is operable.

 

Unfortunately, you can't order just the switch by itself, it has to be the entire shifter assembly (don't remember the part number, just search "G35 shifter assembly"). Try taking off the cover and blasting the switch with compressed air; there could be something getting it stuck. I know that there's some lubricating grease that can get wedged down there from time to time. It's fairly easy to remove the entire assembly, but you'll have to make sure that the linkage arm to the actual transmission doesn't fall and get lost under the car (you'll understand when you see it). It could also be a failing microprocessor (the tiny black boxes attached to the metal switches), in which case you need an entire new assembly (AFAIK, it's not possible to fix those microprocessers).

Worst case scenario it's your valve body solenoids (had the exact same issue). Check your ATF levels and top off if needed. If the transmission has been driven hard while cold/overheated, it can damage the solenoids and make some functions inoperable (my manual mode stopped consistently working because my transmission had started taking chunk out of the transmission housing). You description of it working after sitting for a while points to possible heat problems, in which case you'll want to check the fluid ASAP.

At times the manual mode is just funky; I have a brand new (less than 10k miles) transmission and the same age shifter assembly, and mine STILL refuses to downshift manually under perfectly normal conditions sometimes and once or twice has refused manual mode. It's just the nature of the beast.

 

Check your tcm for codes. It's probably throwing a code but it won't show the check engine light. Mine does the same thing and always stores a code. Manual mode has a mind of its own