2001 sc2 coupe no reverse

[Rooruby]

I’ve owned my sc2 for about 5 years and had minimal problems with it. I’m the 3rd owner of this car and have all service records. Purchased it as a total loss and repaired it.
Last year I started having problems with it smoking when starting. I worked at a GM garage at the time and was advised it need a head gasket replacement. I didn’t have the money at the time but had another vehicle to drive. So I parked “Jersey” until I could afford the repairs.
Recently I was able to make arrangements to have the head gasket replaced. Luckily my brother is mechanically inclined and willing to do it. So tonight I jumped the car ( battery was very dead after sitting for several months). It didn’t sound too bad and stayed running quite well. I drove it to my dad’s to use his garage for the weekend. (Approximately 7 miles)
When I went to back the car into the driveway, it almost seemed like car was on ice and revved up. I pulled forward to adjust the parking job. When I went to put it in reverse again, shifter moved without hesitation but transmission did not seem to engage. However I had drive. There were no previous transmission issues with this car. Shifted fine on the drive to garage- including up steep hills.
Yes, the battery was completely dead prior to jumping. Yes, service engine soon light on dash. I attributed this to the dead battery.
Any insight would help, especially since I planned on getting the head gasket done this weekend and already purchased everything for it

[toggenburg]

This is a duplicate post by the OP on the General Tab.
Have you checked the automatic transmission fluid condition and level?
The fluid should be bright red (not dark), smell 'sweet' (not burnt smell) and up to the fill mark.
These cars need their fluid drained out, and the spin-on filter (in front of the battery, under the snorkel.
Buy the filter at any autoparts store, and similar to an oil filter, wipe the black sealing gasket with transmission fluid before tightening it.
Use ONLY Dexron III transmission fluid....do not use any other Dexron (like IV or VI or whatever else) because those newer fluids are not as viscous (thick) and you run the risk of tranny damage.
Also, these cars usually need their trans drained and new spin-on filter every 30,000 miles. No other car I have ever had required such frequent fluid changes, the doing it will extend the tranny life.
If all is well with your fluid check, then it goes into deeper work, like tranny solenoid testing, etc.

[billr]

Get it scanned for codes. It probably won't help, the diags for the TAAT trans are not all that good, but easy to do and you/we might as well have all available hints.

Lack of R is most often a loose ISN (input shaft nut) or a problem in the VB (valve body); but it won't be anything electrical. You can disconnect every electrical cable to the trans and still should get one forward gear (3rd?) and R. Before digging into either the ISN or VB I would disconnect the shift linkage, at the trans end, and try getting R by moving the shift arm on the trans to the proper detented position.

[termite]

I remember driving my father’s Oldsmobile with a weak battery from a stuck on brake light. I had trouble getting the transmission to go into gear. It’s possible that the battery is too weak for the car’s computer and transmission to work correctly .