2002 Prius Problem After AUX Battery Disconnect *HELP*

Huh, I just did this this past weekend when I had to recharge my 12V battery from letting it get to low from a inverter replacement. Hooked it back up and everything was normal. Where did you disconnect it? At the battery or the cable on the bottom of trunk? I disconnected mine at the cable on bottom of trunk and made sure it did not touch anything.
TomK

 

First, check your connections, if all is well there, by all means shift into neutral and let it run but, there shouldn't be any problems.

 

What it sounds like you're seeing is the "startless start syndrome" that you can find elsewhere mentioned on this forum. What seems like the engine "starting" and then "stalling" a few seconds later, is in fact the engine being cranked and never starting at all. What makes it sound like it starts is that a Prius doesn't crank at low speed like other cars, but at 1000 to 1200 rpm. Then after the short period of cranking if the engine hasn't caught and produced its own power, the cranking stops, and it sounds like it stalled.

I'm pretty sure the whole thing is an 'unplanned feature' (I never said 'bug', now) and shouldn't be expected to make very much sense. If I had to guess, I'd think the engine control module can be put into weird states by glitchy power during its boot-up sequence, as might happen (for one example) if the trunk cable you disconnected was a little jiggly while you reconnected and tightened it.

The one time I had startless start syndrome myself, it was cured after I simply unhooked the 12 V again for several seconds and hooked it back up. I know, I know, that's how you got into it in the first place, but here I would suggest another way to do it:

Look at the big red plastic module that is attached to the positive battery terminal. Two wires plug into it, a skinny one and a fat one, using typical squeeze-to-unplug automotive plugs. Just unplug 'em. It's easier and faster than loosening a screwed-down cable, it's as safe as unplugging stuff at home, and it will give a cleaner, glitch-free power loss.

Wait for many seconds, or a minute or two if you like, for any stored charge in the ECM to be lost, then go ahead and plug both cables back in (I'd suggest fat one first) - just push 'em in smoothly until they click. You're trying to turn the juice back on with a click and not a scrape-wiggle-wiggle.

I can't guarantee this will work for you (I have no insider knowledge of what this bug really is), but it worked great for me, and it makes some sense in a digital-electronics-intuitive sort of way.

The one thing to be careful of is to not make so many unsuccessful starting attempts that the HV battery gets too low to keep going, because that's a difficult situation to recover from. If resetting the 12 V once doesn't do the trick on the first start attempt, I would try resetting once again, rather than making repeated unsuccessful starts.

-Chap