How long would ECU reset last on a bad battery?

So, a couple of days ago I bought a 2005 Prius. But I was a very foolish when I bought it (I'm often very trusting and naiive): I didn't take it to a mechanic, and the seller didn't provide a smog certificate.

After owning the car for two days and driving home around 400 miles almost entirely on the highway, the check engine light, red triangle excalamation, and orange 'Check hybrid systen' all came on. I took the car down to the local O'Reilly's to get the codes read, and they came up with P3000 (Battery Control System Malfunction) and P0A80 (Replace hybrid battery pack).

I am wondering whether the seller of the car may have reset the ECU so that it didn't have any check engine light on, or whether I am just unlucky to have bought the car right before the battery pack started to fail. Is it possible that the car could take that long before re-detecting the failing battery pack?

I intend to take it to a smog place as soon as I can to get more complete ECU information (I understand that after a reset, some parts of the ECU will indicate 'Not Ready' until the car has been driven a decent ways), and have the car booked in at the Toyota mechanic for a complete inspection / to get more detail on the error codes on Tuesday.

Any advice would be greatly appreciated.

P.S. as indicated, I am aware of my stupidity in buying a car without a smog certificate / mechanic inspection. Hopefully I will remember this next time I need a new car.

 

Oh, that smog link is interesting, and good to know. Thanks also for the toyota owners link, I'll check it out too

 

Perhaps the issue is something else.

I drove it down to fail a smog yesterday. Explained to the guys doing the smog that the light was on, I just wanted documentary proof that it couldn't pass smog. Ten minutes later the mechanic comes back to me: "There's nothing wrong with your car, that's just the oil change light (The maint required)." "Nah that can't be right, the check engine and exclamation was on while I drove down here..." so I hop in, press the power button... and everything is fine. Ok. So I got it smogged.

Today, driving, the dashboard lights up again with the Triangle excalamation mark, check engine, and also the brake control system ((!)) warning light. But it's still driving alright, and I've got an appointment in the next town over, so on I go. No problems, but next time I start the car the dashboard won't turn on and the energy/consumption screens don't work properly - but it still drives fine. Then it won't turn off - but again, still drives fine. Finally I get back home, and it turns off fine, then turns back on and the dash and everything is working (although it hasn't recorded the last 40 miles while the dash was off) but the check engine and red triangle are still on.

I understand that the best idea might be to try reverse the sale. I can also imagine that might need me to go to small claims court - so if it turns out to be a fixable problem, I would prefer to do that.

Perhaps it's the 12V system? I don't know. I cancelled the appointment at the dealership when the problem spontaneously resolved, but now I've got another one on Thursday. Hopefully there's actually a problem for them to diagnose when I bring it in.