How many miles on car?
Does 2md gear act normally?
What is the fluid level?

Reverse requires a higher line pressure in the transmission to engage than the forward gears,

 

 

Does the vehicle shift hard ("slam" ) into any gear and if it does /did, did it slam into reverse?

 

 

Sorry for the delay.

See

https://www.sonnax.com/tech_resources/289-saturn-taat-reverse-issues-should-you-replace-the-valve-body

for a nice explanation of scenarios which result in a no reverse condition. In summary, I'd get a quality rebuilt valve body, a new input shaft nut, but check the VSS first. If you drive it long enough you will eventually need both the valve body and nut. I would take the plunge now if the VSS checks out ok since the parts may not be available when you need them later.

 

 

Suddenly losing reverse in these transmissions (TAAT MP6, MP7 - these are the ones used in the S series) is most likely going to be the result of a failure of the solenoid valve that controls reverse. A gradual failure could be the valve itself wearing out (valve body) but a sudden failure is going to be electrical meaning either the solenoid isn't getting power (broken wire or corroded connector) or the solenoid itself is either shorted or has a broken winding. It's common for people to go with conventional wisdom and use stop-slip or try the "reverse slam fix" but this is normally a problem that will only be corrected by physically replacing or repairing the faulty part. Fortunately these issues are relatively easy to fix and don't require pulling the transmission or insane acrobatics. If the transmission is allowed to slam into gear though, the input shaft nut WILL work loose sooner rather than later and that will be harder to fix and require a special socket and bracket but still be fixed without pulling the transmission. A sign of the input shaft nut working loose is having no 2nd gear. That's why when someone says they lost reverse the first questions after "got proper amount of correct fluid?" are was it slamming and did you also lose 2nd gear.

That Sonnax link Derf gave you is an excellent source of information and parts on these transmissions. I highly recommend checking them out even if you don't plan on buying anything from them. I fixed my transmission with used parts sourced locally using knowledge gained from their site and this site: Saturn S-Series Transmission Repair Kit - CarSaturn