2004 Prius no ready mode, check engine light, no codes, accessory mode on

Hi there,

I did a bunch of searching and didn't see any posts with this particular error. I'm at a loss, and hope someone can help. (None of the mechanics I've been working with, not even Toyota's own mechanics, have seen this before, either, so its time to ask the internet for help).

In short, my 2004 prius (150k miles, I've owned it since 2009) is intermittently not starting. Sometimes it is completely fine, but sometimes I'll go to start it, and it will briefly show the check engine light and then turn on the center computer/accessory (including the radio, etc), but the car itself will not start. Another push of the power button turns everything off. No error codes are stored in the system, and of course, every time I get it to the mechanic, it behaves perfectly for them.

The only "trigger" it seems to have had is that I'm in the process of moving, and both times it had this issue (over a week apart), I had the back seats down and the car filled with stuff (~100-200 pounds spread over the back). The first time the issue happened, I emptied the car to prep for the tow truck, and 45 minutes later it started up/drove just fine. The second time, it did not get better with emptying, but the next day I had it towed, and the tow driver was able to get it started and in gear (no dash lights came on though), and then wasn't able to turn it off for 10+ minutes. No rain/water, no extreme temperatures.

First thought is that there's a loose wire somewhere in back connecting to the hybrid system and putting pressure from some angle causes it to short, but no one seems keen to troubleshoot that. Second thought (from discussions here on the forum) is faulty combination meter, but they say that is unlikely because that would leave a code. Video of the issue is below. Any ideas would be welcome.

p.s. The car otherwise runs perfectly, the hybrid battery is in great shape, it just got a new starter battery after I accidentally let my previous starter battery die during an extreme cold snap that corresponded with major surgery and I didn't drive it for a month. However, it has a slightly haunted electrical system - the previous owners put an after-market radio in it and that has caused some issues in the past with battery draining. It also went through a 2-week period where it would randomly have the alarm go off (thankfully that stopped), and there was also an interval where pushing the power button would cause major shock/shorts - luckily that stopped quickly too. No one ever figured out what was happening with any of those issues, but I do think my electrical system needs some help in general.

 

There are no codes - unfortunately it just gets stuck in this "not-start" loop and doesn't save codes. (This has been elevated from the regular mechanic to the dealer to a level up in the dealer - we've been looking for codes with the correct tools available for weeks)