2003 Prius P3000 code

This can be a can of worms. I'd not think that reflashing the battery ECU would help. Do you have a code reader that will read the sub-codes?

I'm also fighting a P3000.. In my research the problem may, or may not be a problem with the HV traction battery. The manual tells me that there's a problem with the HV battery. Here are the areas that the manual centers on if you've got a sub code:

• 
  HV Battery System
• 
  High Voltage Fuse
• 
  Power Cable
• 
  HV Battery Cooling System

I've now been able to define that the problem is a P3009 error. That's a problem with leakage to ground from

• The HV battery, or
• The HV battery cables, or the
• Electric Motor

All I have to do now is narrow it down. I'm hoping it's leakage in the battery and I can clean up the terminals and get some more life out of it.

I'm still doing more research on this to narrow it down further...

I do have a 2nd problem that the auxiliary 12 volt battery dies if the car is not driven every day. The battery is new, and it is good. I've two 2002 Prii that I can swap the batteries to see if the symptoms follow the battery. The problem does not swap to the other car, so the battery is good and the car has a parasitic drain.