My 2001 Subaru Outback Legacy Sedan won't engage in forward gears.

as a d.i.y. person there is one thing I learned; stock answer that you will get is that you need a tranny overhaul. Without a service guide you won't even know the set up of your tranny,the auto mechanic will guess and the transmission shop is your last hope. I could ;but,won't take you through the month long journey I went through to weed my way through myth and mystery surrounding trannys;until, I found out the set up of mine and how to fix it externally. Unless you have countless hours ;the cheapest thing to try is to drain the tranny a few times and put in a new filter. Stay away from stop leaks because they soften the seals and don't really fix anything. If after new fluid you get no difference then [electronic trannys have solenoids inside them] a solenoid may be the problem.

all trannys are different - with mine selector set to D1 is 100% electronic so I put mine in D1 and it worked fine. Then it has a manual hydraulic override of the electric for selector level in D3 or D2 position regardless of the shift solenoids. That's just mine - all are different..

If it is a manual with Hi / Low range selection, you may have bumped the Hi / Low range shifter into the neutral position which stops selection of forward and reverse gears.