2008 won't start after sitting for 2 weeks. CM, ECU, or Hybrid battery?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by PriusOwner428, Sep 17, 2025.

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PriusOwner428 Junior Member

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Feb 5, 2022

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IL

Vehicle:

2008 Prius

Model:

Base

ChapmanF said: ↑

It gets some decision-making inputs from sensors in the hybrid battery. It uses those inputs when deciding about going READY. It doesn't care about them at all when deciding to go IG ON.

The power to make all its decisions, it gets from the 12-volt battery.

IG ON does not require anything from the high-voltage system at all. As long as you can go IG ON, the ECU will have power, you can examine it with a scan tool, and you can even see what its inputs from the traction battery are showing.

If you then request to go READY, the ECU will either do so (if all the required inputs look acceptable), or it won't, and the warning triangle will light up, and the trouble codes will tell you why.
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OK thanks. I think this helps me get a better understanding. I think what you're calling IG ON is what I'm calling ACC. It's what you get when you push the power button once or twice without depressing the brake. It powers your radio, windows and cigarette lighter sockets correct? So with the hybrid battery not being the culprit it's looking more likely like a mouse.

#41 PriusOwner428, Sep 27, 2025 at 6:12 PM

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