Hybrid system error but clears for week or more with battery reset

The code is a bad hybrid battery. 99% of the time there is an additional code that tells you what the problem is.

Remember the car doesn't really have much information on the battery. All it knows is the current block voltage (12 cells in series), total pack voltage (all 28 modules in series), the current in and out of the pack, and the temperature of 3 spots. That's it. It tries to guess state of charge by counting the energy flow into and out of the battery, but that's a calculation.

As you drive around, there may be times when one block has a too large a delta between it and the rest of the pack and that throws an error that the module is too low. Or the other way, those bad modules also throw codes of being too high versus the rest of the pack during regen or charging. This also heats up the cells and it could throw a temp code. But most likely you have voltage variation problems.

Once you get a code like that, the car limits the power from the battery (to basically nothing) and you're driving a VW beetle engine pulling a few thousand pound vehicle. It isn't going to go well. The Prius needs the battery to work anything like a normal vehicle. What you're experiencing is completely normal. Now this error code is in the moment. If you give the car amnesia by pulling the 12v battery all is well until it comes back.

The fact that it has come back multiple times, means you are driving on borrowed time. You can usually go weeks, sometimes months, generally less than a year from when the codes start to when they just won't go away anymore. In the mean time, you risk having the battery in the back pop. Literally explode and vent fumes. The chances of that happening go up the more and more your drive it while it is failed.

Your options are to:

a) junk the car
b) replace the failed module with a close-as-possible used module. Then welcome yourself to the game of battery module whack-a-mole.
c) replace the failed pack with a used (aka refurbished/rebuilt) pack and expect to get a year or three out of it hopefully. Lots of horror stories about 3-6 months. Sure it's under warranty, but your car is out of service for at least a few days every few months...
d) replace the failed modules with brand new DIY modules (see sig link, you have to swap batteries, you keep your old electronics)
e) replace the failed pack with brand new DIY Toyota pack (you have to swap in your old electronics, batteries come pre-installed)
f) replace the failed pack with a brand new dealer installed or trusted hybrid mechanic installed Toyota pack

The clock is ticking.

 

What in a modern car doesn't?

You scratch the paint, that's over a thousand dollars. You do a jumpstart backwards, that's over $4k to fix generally.

(a) is free. But you have no car.
(b) costs $40 a pop and LOTS of your time every few weeks/months as more fail.
(c) costs between $600 and $2200 depending on how good you want it to be.
(d) costs $1600.
(e) costs between $1600 and $2100 plus a $1350 core charge and tax
(f) costs about $2500 to $3200

These are averages I've seen around the US in 2019 in USD.

 

Because you can't do the swap at the parts counter. Even if you do it in the parking lot, not advised, you still have to pay the core charge.

 

maybe time to move on. even if you replace the battery, you still have the inverter, brake actuator and ego circuit in front of you. unless they've already been taken care of.

 

If you can't service your vehicles, then it's time to get something newer.