You would be better off if you got a OBD-II scanner that works on a laptop that has MSwindows
You can buy one like at Amazon for less then $100 as that would be far more useful and more information then using the DIC of C5.
Review all ground points in this post C5 Ground locations
You state problem began when hitting a hard bump, so it sounds like something got loose.
You need to be sure the battery cables ( at both ends of each) and it's posts are clean and tight correctly, including the one right below battery and the flat braided on on back of left side of engine.
Are you sure the battery is good ?, a weak cell would cause all kinds of odd problems, with engine at idle the volts gauge in dash should be showing 14 plus volts.
As I mentioned model years 1997 and 8 are odd as 1999 had many changes
Depending if your 1998 was made early or late in build would have changes, one is the EBCM controller for ABS/TC, etc
It could be located in front if late build, if not then it is in the back end, would have several brake lines attached to it
I would check to see if the wiring connector is firmly on, else look for any wiring damage.
It could be the wiring connector for it is loose or a wire got pinched.
Look at the 2 posts in this C5 techie sections here for both fuse panels
For the engine one make sure the 12 volt wire on side of panel is firmly connected, that is main 12 volts for controllers
Make sure no fuses are blown.
In the hatch of passenger floor is where other fuse panel is but also the BCM, most wiring and the car's Star bus network where all the controllers connect together
I would check fuse panel, all connectors, including the ones for the network are firmly connected and that no animal has eaten wires
The PCM is behind the right front inner fender facing firewall, there is a hatch space that allows part of that to come off and there PCM is plus the main wiring loom
PCM has 2 80 pin connectors, assure connect pins are clean and connector tight.
Check wiring there for a animal eating wires or in past the battery leaked acid and got onto the PCM or wiring.
Check wiring at the starter, there is a 12 volt wire, if loose would cause odd voltage issues.
Maybe with someone else with key on, engine off is one of you move or tug connectors and other person see if anything odd shows up