Wont crank and 12v is ok. Lost.

I'll preface this by stating I am far from experienced when it comes to Gen 1. That being said:

Is there a check engine light?

Red Triangle of death?

Does dashboard remain fully lit the entire time?

 

The 12v system supplies the power to operate the main relays for the HV battery. The main relays are located inside the HV battery case.

A few quick possibilities:

12v is too weak to maintain the relays closed.
A loose connection is interrupting 12v power to the relays
Bad relay
A safety signal is telling the relay to open

 

Once the relays close, the DC-DC converter takes over the 12 volt supply, so weakness of the 12 volt battery becomes kind of moot at that point as a reason the relays opened again.

I would begin investigating with the fourth choice above: the car powered down for a reason, and will probably tell you what the reason was, if asked with a Prius-capable code reader.

Inconveniently, almost all of the computers in Gen 1 can give you codes with no reader tool at all, if you're willing to count some light blinks, but the reason in this case is probably stored in the HV ECU or Battery ECU, which don't have light blink options and only talk to a reader tool.

The gold-standard, plug-it-in-it-just-works option is Toyota Techstream, but thanks to a lot of work by vincent1449p and others, it is possible to make some other tools work and at least retrieve basic info from those ECUs. A ScanGauge II can do it, and probably the Torque app, if you're willing to load some car-specific definitions in.

-Chap

 

Check your 100A fuse in the engine bay. Top right corner.
Inside the fuse box itself, it's on the top left corner.

I didn't read this whole post in detail, so this may not be it, but on the surface it sounds similar to an issue I had.

I accidentally reversed the jumper cables on my battery once. Car wouldn't start after correcting it. It would act funny and made no sense.

Found this 100A fuse blown. It's a bolted in fuse, not a normal pull-out.
If it is blown, then you need to do some surgery to get access to the bolts, to unscrew the nuts that hold the fuse in place.

In my case, I destroyed the fuse in trying to remove it, not realizing it was a bolt in.
I had to remove the whole fuse box assembly to remove the bottom cover to access the bolts.
The cables that go to the 100A fuse are thick, as you can imagine, and don't have a lot of flex or slack.

 

What;s the calculated state of charge of the traction battery? That's something you can get from lots of readers, Torque phone app, etc., if you plug in the right PID definition.

-Chap

 

I can verify that Torque Pro will tell you this, when used with a generic Chinese Bluetooth OBDII reader. (I don't think regular Torque can do it.) Get the PID definition file you need from this post https://priuschat.com/threads/scangauge-or-torque-app.120091/page-5#post-1752194 , edit it as described in this post Scangauge or Torque App? | Page 7 | PriusChat , and load the edited PID definition file into your phone/tablet.

 

P3191 iis the code for "engine did not start". You thought it started and ran for 20 seconds, but it was only cranking for that time and trying to start; this fools everybody, because MG1 cranks the engine so fast it sounds like any other car's engine starting. But the P3191 is telling you the straight story.

What is the state of charge of your traction battery? Every single 20 second cranked-didn't-start attempt is going to cost that a percentage point or so. So you have a limited number of chances to figure out what engine issue is making starting difficult. If the battery charge gets too low to crank any more, your car will be an expensive landscaping ornament until you get hold of a high-voltage charger and several hours to charge it back up.

-Chap

 

Usual engine stuff. How's the compression? How's the ignition? How's the fuel delivery?

I don't know a really easy way to check exhaust back pressure (plugged cat?), but yeah, that too.

-Chap

 

If the engine isn't able to run consistently and produce power, there won't be much or any charge back to main; rather, power will be used trying to keep the car moving and nursing the stalling engine along.

Why is the engine running so poorly?

-Chap

 

320v would be 8.4 volts per module. That's probably 100%+ charged.
260v would be 6.8 volts per module. That's effectively 100% discharged.

How are you charging the HV battery?
Was it charged while installed in the car?
Was that 320v measurement taken immediately after disconnecting the charger?
Was the test drive performed immediately after the battery charge or did the battery sit for an hour or two?