Prius 2008 won't start - not the 12 volt

I have a 2008 Prius that is my daughters car. She called yesterday saying that her car won't start. Thinking the heat here in Phoenix had killed her 12 volt battery, I went to rescue her with my small battery powered jumper device that I have successfully used in the past.

That didn't work. So I used jumper cables from my car to the jumper port in the engine bay. That caused a significant spark. I did positive to positive and negative to negative. I finally had her car towed to my garage so I can troubleshoot it in the shade.

Here are the symptoms:
What does not work: The car won't start. No dash lights come on except the check engine light and the door light. I have to insert the proximity key into the dash port to get it to do even that. When I push the power button with my foot on the brake I can hear pumps engaging in the engine bay but nothing else happens. The break lights don't work. Nothing else in the dash works (stereo, fans etc). I can't connect to the ODB-II as it doesn't seem to be getting any power.

What does work: The emergency flashers do work. The dome lights do work and the headlights do work.

Here is a run down of everything I have done so far:

Taken the 12 volt battery out and had it tested. It tested fine.
Replaced the 120 amp fuse that was burned out probably from the faulty jump start attempt.
I have checked every fuse in the engine bay.
I have checked every fuse in under the dash.
I have checked the IG1 relay against a known good relay.
I have checked all the relays in the engine bay fuse box against known good relays.

I have officially run out of things to check. I'm very handy and have done A LOT of work on this car over the years including replacing bad cells in the drive battery by myself. I know this car well, but this problem has me stumped. I hope someone out there can point me towards something I may have overlooked. Otherwise it will have to go the the shop.

Thanks!

 

Thanks.
There is no way to read the trouble codes as my ODB-II scanner can't connect as there is no power to it.

 

I've done that already. Twice in fact, checking each fuse for continuity. I'm wondering if it is the ECU module? But would that cause the brake lights to fail to come on, while letting the flashers work and the headlights to work?

 

It was odd that the jump start caused a significant arc. There is no evidence of rodent damage.

 

Yes. The interior fuse block has been checked. Including the relays on the same block. The 120 amp main fuse has been replaced (it did burn out when it was jump started). And the small 5 amp fuse checks out fine on the positive terminal block.

 

I thought of that, as I have replaced the combination meter in the past. Completely different symptoms with this. The ICE won't start even after a good amount of time. Nothing happens without the key fob inserted into the dash, so the proximity key isn't working correctly. I also get no communication / power on the ODB-II connection. If the 120 amp fuse was blown again the car wouldn't get any power at all.

What is mysterious is that the brake lights won't come on. The fuse for them is fine and is getting power. I would have thought Toyota would make the brake lights a direct connection (not going through the ECU) similar to the hazard lights or head lights. The only thing I haven't checked is the ECU itself. If it is bad, could that keep the brake lights from coming on? It may explain all the other symptoms so it is my best guess at the moment. I'm not looking forward to removing that.

 

I considered that. It is a possibility I suppose. However that wouldn't explain why the ODB-II isn't getting power, or why none of the dash lights come on even in ACC mode.

 

Thank you! This helped a lot! I never thought to check that and indeed it is blown.

I'll jump across the link to make sure it is the problem. I'll report back if that indeed fixes it!

 

I'm happy to report that one of the show stopper problems was indeed the fusible link. Thanks TMR-JWAP! Once that was solved, I was able to quickly troubleshoot the other minor issues and got it running! 309,000 miles and my daughter will be able to keep her car for the next 6 months or so until she graduates high school.