Not starting

That sounds a lot like a bad body control module.I have seen them go bad and cause those symptoms and cause you not to able to talk to the ecm.I have never tried unplugging the throttle body to see if anything changes from doing that.I have a whole stash of old bcms for testers with the symptoms of what they doing when I changed them to see what changes when I plug them in. What you say about the gauges and not being able to get it out of park are all known things I have seen happen when bcms on those cars go bad.

The bcm is on top of the glove box you have to remove the glove box and it's attached to the glove box.I have also seen bad bcms cause no starts when the gauges etc are inop. Then when the gauges work the car starts. Bcms are close to 300 plus they have to be programmed.I have seen a repair service on eBay that is much cheaper plus it keeps all your day mileage programming etc. You mail your bcm to them and they fix it and mail it back. It was very reasonable verus buying a new one and having it programmed. As far as testing them we never tested them at the Saturn dealer we just swapped it for one of our old ones we replaced and saw if it changed the symptoms. It's very common for them to go bad that's why I asked about the symptoms. Which you mentioned the ones I asked you about. You may have more than one problem but it sounds like you have a bad bcm.

1-866-573-2740 that's the phone number for the bcm repair service call them to talk to them about your bcm.

Here's my problem with that theory not being able to take it out of park is controlled by the bcm not pm. Also if the car will only start when the gas gauge works another symptom of a bad bcm.I have replaced tons of bcms on those cars or tons of ecms. The number I gave you the guy charges 165 to repair the bcm. Go to eBay put in the search box Saturn bcm repair it will come up. Read the listing and symptoms and then post back to me and tell me what you think.

I told you where the bcm was it's mounted to the glove box insert. There are multiple philps screws on the inside of the glove box. Also take all the screws that hold the glove box door out. There is also a AC duct hooked to it if memory serves right. It's been a lot of years since I have replaced one.

It looks like they went back and fourth for a while. can I ask if you have any codes and can you hear the fuel pump run in the tank when the key is in the on position?

This guide can help us get started:

https://www.2carpros.com/articles/car-cranks-but-wont-start

Please run down this guide and report back.