Your contacts on the battery wire are dirty and loose .. Try cleaning them ( there is a cheap post cleaner tool you can get... ) also check the ground ( the black wire going from the battery to the car). Check where it attached to the car to be sure it has a tight contact and is clean..,battery wires wear out and are not expensive to replace. You can tell when it's time by lifting the plastic on the end of the wire and see if its green... the more green the more corrosion and it's time for them to retire.
I think you could use this manual method instead.. My nephew who is a full time mechanic uses most of the times, and all mechanics look up to manuals. It's very easy he gets it from. www.reliable-store.com all the best
The E-brake just needs adjusted up on the pads or rear shoes. If shoes on the rear instead of pads, it will hold from rolling back but not forward if not getting full pressure from the brake shoes needing adjusted up closer to the drum. It will hold from back roll because of shoe design. More shoe surface on the rear shoe than on the front shoe. That's the way they're built.
The PCM is probably storing a B, C, or U code that your code reader doesn't read. Or, it's storing an enhanced P code. If the light goes on, trust me, there's a code stored. You need a professional level scan tool
Doing electrical circuit testing of the thing's not working would be the way to find the problems . Not looking for magical fixes on here . Without testing anything said on here would be guesses . Are prepaired to replace a bunch of parts till it's fixed . Do you know how to do automotive electrical testing using a wiring diagram and a DVOM - digital volt ohm meter ?
This is why repair shops charge what they do . Takes years of learning (training ) to get good at testing electrical systems. Plus the amount of tool's required. $$$$$$$$
The fuel gauge or the sending unit could be the problem or the insturment cluster . Testing ,hooking up a scan tool that can read codes in the insturment cluster , that can read codes in all the modules on the vehicle.
Clean the surface of the ABS where the brake lines attach.Some are stamped beside each line connection with LF ,RF, RR, LR, master cyl input front, master cyl input rear if yours is a stand alone unit.Otherwise you will have to follow the line back from your RF wheel to the ABS unit to determine which connection is for the RF.