Could be a few things. But as a starting point try these tests.
With the engine cold, pull the transmission dip stick, does the fluid show on the stick in the cool area? Is it clean and red and smells like oil, or is it dark and smells like burnt oil?
If the fluid does not show on the stick buy some of the proper fluid (Dexron Type II/III) and add some until it shows in that cool area with a cold engine. If you have to add a lot (over a quart) of fluid, check your engine oil level, I am not doubting anything but I have seen people accidentally drain the wrong pan before. If the engine oil is okay but you needed a lot of fluid you may have a leak.
So you do all that and still no forward gears:
Jack the car up and put a jack stand or two under it.
Now either video or have someone watch the shift linkage as you shift through the gears. Does it all move correctly? I am going to guess that it does.
So for the next test, Unplug the large vertical wiring harness plug on the drivers side of the transmission. It is a very tight area to work in and there is a small brace that is usually in the way. (Having hands the size of a five year old helps in this but most of us do not have that option). Once that is unplugged, put the car back on the ground and see if you now can manually shift it and have it move.
If yes then you have an electrical/computer problem. Plug to connector back in and you will probably want to take it to a shop. Electronically controlled transmissions can be very hard to track problems without the proper scan tools and test charts.
If it still does not move the problem is likely the forward clutch in the transmission, that is a rebuild/replace type repair.
Wednesday, January 11th, 2017 AT 11:45 PM