2003 Prius 12v battery draining, not charging

With the car running, my voltmeter shows that my 12v battery is draining about .1 volt every 2 seconds. I'm able to drive the car for 3-4 minutes (before dash blinking starts and car dies). From reading the forums, it sounds like my inverter or dc/dc converter has gone bad or I've blown the 100A fuse or perhaps the inverter pump has gone bad.

So, I'm trying to test the fuse (see pic 1), hoping for the best.


I've read that I need to lift out the fuse box to test that fuse (true?)
I found the two fusebox mounting bolts (see pic 2 and 3) and was able to remove them.


I disengaged the clip (see pic 4).


However, as yet, I'm unable to lift out the fusebox.
There is a cable (assuming wiring to fuses and relays) preventing lifting (see pic 5).


Before I get too much pulled out, I thought I'd ask if I'm proceeding correctly.
Is there a better/easier way to test the fuse or dc/dc inverter?
I don't currently have an OBD II but I've ordered one.
Help, please.

 

Possibly, but it's new (1 month). I've drained it down to 10 a few times. Charges up to 13+ volts with external charger. With engine on (in Ready mode), I use a voltmeter to test across the battery. I'm expecting to see something similar (13+ volts) but I see the voltage steadily going down, as noted in the post. So, I'm thinking the 12v battery is not being charged.

 

Update: To test whether the inverter is charging the HV battery, I connected an OBD II plug.
I can see that the HV battery is charging (and discharging) when the engine is running.
The pack voltage increased substantially (290 to 310) so I'm fairly confident that the
inverter is working.

Still troubling is why the 12v battery is not being charged. My understanding is that the
dc/dc converter steps down the HV to 13.8.

How can I test the main (100A) fuse?

 

Great suggestion, ChapmanF. I had (wrongly) assumed that the dc/dc converter would charge
the 12v battery and the 12v battery would power the various 12 circuits.
I appreciate your specific information (CDS fan fuse should be 13.8ish); that is just what I needed.
Thanks for providing the link to help find the wiring diagram - a wiring diagram will help me figure out other things in the future.
Great post!

 

Update:
1. The car does not start with my OBD II plugged in!
I pulled out the OBD II and started the car.
The OBD II reported p1636 but after clearing, it didn't return.
I imagine (I need to test) that if I try to start the car with the OBD II inserted, p1636 will return.

2. The voltage at the CDS FAN fuse is 13.93.
So, I'm thinking that I can reasonably assume that the inverter and converter are working.

3. The voltage at the DOME fuse is 11.45.

By visual inspection, the main 100A fuse looks intact. However, considering ChapmanF's comment,
"If that fuse were open, for example, you would see converter voltage (13.8ish) at places like the CDS FAN fuse,
or ABS NO. 4, but see battery voltage (12ish) on circuits like ABS NO. 3, AM2, or DOME."
If I interpret this correctly, I need to replace the 100A fuse.

Now, the question is, "How do I get to the bolts/nuts to replace the fuse?"
Does some part of the fuse box lift out? Do I need to lift out the entire fuse box?

 

Update:
Upon closer inspection, with some adequate lighting, the main 100A fuse appears to be open (see pic).


I think I found the relevant page in the electrical wiring manual (see below).
The green annotation show the connectivity from the converter to the CDS FAN fuse.
The red annotation shows connectivity from the battery to the DOME fuse.
If the main 100A fuse is intact, the red would be at the same voltage (~13.8) as the green
since there is connectivity and ~13.8v comes from the converter.
However, if the main 100A fuse is open, there is no connectivity so the DOME fuse
would be at the battery voltage (decreasing from 12.5 over time).

 

Yes, thanks to you, ChapmanF.
I figured out how to get that assembly apart and the fuse out but, you're right, it was a task.


I couldn't find a relevant thread for Gen 1. If you happen to have a link, please post it here.
Perhaps I can document the procedure when re-assembling.
Now, I have to go find a new fuse.

 

Perhaps a senior member or the forum master can help.
There are main forums for 4th Gen Prius, 3rd Gen Prius and 2nd Gen Prius.
The 1st Gen Prius is kind of a sub-forum under 2nd Gen Prius.
This is a bit confusing and Gen 1 things that I search for return unwanted Gen 2 items.
Can we create a main Gen 1 forum?
Then, we can migrate Gen 1 items out of the Gen 2 forum into the new Gen 1 forum.