Over night power dies, backup starter kicks in but car in some brake mode

[samwichse]

The brake light always comes on in lockstep with the battery when the 12v system has a problem, no idea why, but you probably have no brake problem.

1) Check the 12v battery
2) Check the 4 ground straps in the engine compartment.
3) ???
4) Profit!

[juntjoo]

What does it normally use to start the engine? The ima system no? isn't it a backward response to use the starter with the weakening 12v or is it doing it to communicate to me there is a problem? And I did put it up on jacks and in neutral and the front wheels felt like they were "in gear" but stationary rather than idling -with the car on of course. Thanks

[samwichse]

Basically, it all goes to hell if your 12v is weak or dead or poorly connected... there's a big fat relay in the back to turn on the high voltage system that needs a strong 12v source to work, and I think if it fails to close properly, the car basically says "uh oh, no IMA power, have to revert to 12v starter," but of course the 12v is weak, so...

Also: are you saying your brakes are siezing?

[juntjoo]

Hmm.. Well this morning I did something different, and no, no brake seizing at the moment. Let's forget about that. Perhaps I imagined that -maybe. But anyway, this morning the usual one Mississippi two Mississippi count didn't work so I just drove to work with it in gas only mode and about half way there I heard that relay kick in and viola it was back to normal, so I guess you're just supposed to drive normally and it fixes all on its own. But I guess I've got a 12v system issue to diagnose.

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[samwichse]

That sounds like a bad ground problem for sure.

[Need4Speed]

If your 12 volt battery is too low, it will start off of that one instead of the big hybrid battery (even if the big battery is fully charged!), and will start using the regular slow starter.

I don't know why it does this, but they all do.

With normal starting from the big battery most people don't realize that their 12 volt battery is going bad, until the car doesn't even start off either battery....

[juntjoo]

Hmm.. I guess I assumed the 12v system was backup for the ima. Apparently not uh?

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[juntjoo]

Well it turned out to be a bad battery. That's all. So I guess when it dies the car let's you know by not starting -or maybe the system users the 12v battery to start the car. Yeah, I think that is how it works

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[eq1]

I think what most people are saying here is that, when there's an IMA problem, the car will start off of the 12 volt battery and 12 volt starter, rather than the IMA battery and electric motor. Yet, one of the problems with the IMA system can be the 12 volt battery itself. So, as you said, kind of backwards, because reverting to the 12 volt battery and starter isn't going to help if the 12 volt battery is bad... Anyway, sounds like you got it fixed. Good deal...