I have a 1990 Civic with an automatic transmission. Once vehicle warms up and I have driven about a mile, the vehicle behaves like it slips into neutral. I can move shifter into other gears or reverse but vehicle behaves like it is in neutral. No noises, clunking, grinding, etc.... When I turn vehicle off and turn it back on, I am able to shift into gear and drive for about 50 yards. Once it begins to shift again it happens again. I played this game last night to drive home 3 miles, turning vehicle off and on each time to continue down the road. No check engine light and the error code indicator lights located under passenger side carpet does not display any error codes. It behaves more like it is a sensor issue rather than a transmission issue. I'm desperate for feedback because I need to vehicle to commute 30 miles one way to week. Any help would be greatly appreciated.
Thanks

 

The first three gears are entirely mechanical IIRC. The computer is only involved for overdrive and torque converter lock, both of which only occur at highway speed. Is the fluid level OK? It is probably a clogged filter or other mechanical problem in the transmission.

Also check if the speedometer goes up when you try to go forward but the car is not moving. That will happen if one of the CV axles has disengaged from the transmission.

 

Fluid level ok. I changed fluid this morning and drove it. Get up to highway 60+ after driving 2 miles it happens again going from 3rd to 4th. Can shift car to any gear but I have nothing. Turn car off. Start it again, all gears work. I drive the remaining distance home gently in 2nd.

Drain and change fluid again. Get car up to 60+ slow down to turn around and it does it this time going from 2nd to 3rd at low speeds. Turn car off. Start it again, all gears work. I drive the remaining distance home gently in 2nd.

Speedometer behaves correctly during all events.