2005 - Dying Accessory Battery... wait a minute... huh?

You have to first address the low charge on the 12v battery before you can diagnose any other problem. So if you have a battery charger that charges at low amperage, you can charge the 12v to full and then see if it'll hold a charge. At the current state of under 12v, it's basically a dead battery

 

you could have allow it to drain by not driving long distances, short distance driving (like a mile or 2 a day) will not charge the battery properly

 

could be under warranty, get a free load test at most auto parts stores

 

You have some misunderstandings as to how the 12v system works in the Gen 2.

First, your 12v battery is very weak right now, whether that is from a failing battery or from not enough use is yet to be determined. What are your normal use habits for the car? Even a brand new battery will drain almost completely in about 6-7 weeks of low/non-use due to normal shutdown current draw of the cars systems. This can be extended by deactivating the SKS system using the button under the steering wheel labeled "KEY".

Second, when you see the 14 volts, that is not the 12v battery, that is the DC-DC converter powering up and taking over the 12v power system. This happens when the car goes to READY mode, where the HV battery is placed on-line and HV power is sent to the inverter systems. Similar to how alternator in an ICE car comes to life when the engine starts running.

The pending P3014 means "Block 4 becomes weak", which means block 4 (of 14) (or module 7 and 8 of 28) in the HV battery at one point in the recent past exceeded the threshold for the code. If it happens again within a certain timeframe, it will RTOD and go to a limp mode style operation. Usually, this "pending code" is an early clue of upcoming HV battery failure.

 

1. If you lasted 2 years without doing anything to the battery, then you probably don't really need a trickle charger. You just need a battery charger that can top off the battery once or twice a year. Hook it up at night, by morning, it'll be fully charged. Do it Jan and June of every year and you shouldn't have any issues. I use a very high quality one from CTEK. It's a trickle charger and battery charger all in one. And it has the important AGM charging function, for all the Prius batteries (and other cars) that are AGM

CTEK - 40-206 MXS 5.0 Fully Automatic 4.3 amp Battery Charger and Maintainer 12V


When you get your new replacement battery, try to charge it fully before installing. Then it'll be fully charged from day 1

 

When you say 'main computer', you're talking about the display in the center of the dash/center console above the radio, right? It sounds like you're describing the screen being burned out. Kind of like a circular or oval discolored area in the middle of the screen? Those are actually fairly easy to replace if desired, but it's important to get the part number from the back of it, so it can be replaced by the same.

 

That thing you want to buy for under $40, has a retail price of over $4000 from Toyota.

You can get it repaired for about $300, or if a junkyard has one, it'll be around $150 - $200

 

Nope. Every minute the battery spends below full charge increases the sulfation (slowly) and the farther the battery is below fully charged the faster it will sulfate. Overcharging it will screw up the battery via other mechanisms eventually, including corrosion. So for longest battery life having a good battery maintainer (carefully sticking to float voltage once charged) on the car pretty much all the time it is off is the way to go. A deep discharge, and 10V is like 0% SOC, will damage an AGM battery permanently. The Prius battery is not a deep discharge battery, even going below 50% is a bad idea. This is one of the advantages of the deep discharge batteries discussed in the "Mobility Battery" thread, they are designed to be very deeply discharged without sustaining (as much) damage. Anyway, ignoring a Prius battery for three weeks or so (not driving it at all or too little) will damage the 12V. Full charges twice a year will not overcome that problem.

SOC isn't the whole game though. Heat kills batteries too, the more heat, the shorter the lifetime. I imagine S.C. is pretty hot for a good part of the year, albeit not Phoenix or Death Valley hot. Driving in hot weather with the AC not on can really cook the auxiliary battery, especially if that side of the car is in direct sun.

 

When in doubt, step one is always to fix the most obvious problem first. First, your 12v battery is very weak right now. A 12v battery that isn't at least 12v is the most obvious problem in your list and can create additional ghost problems. Whether that battery was faulty or just needed charging, we'll never know. It sounds like you're getting that resolved currently with the new 12v battery, so that's great. When you swap the battery out, unless you use a maintainer to keep the 12v circuit alive, you'll clear all codes in the ecus and reset all learned parameters back to original default values. At that point, all you can do is drive it and see if any codes return. Hopefully not. If they do, at least you'll know they're legitimate codes.

As for the other information in the post, it's important to understand how the 12v system works for accurate troubleshooting. I was just trying to clear up any misunderstandings.

 

A good idea. Last thing you want is to have to deal with a hungry vreak.

 

Surprised no one suggested a parasitic draw test... excessive draw when shutdown can kill a two year battery and can do the same again.

Often people who have the test run or are proficient enough with a amp meter in the milliamp scale find an aftermarket accessory like a gps or amp or an obd2 reader stuck in by the owner or an insurance company was the root cause.

 

If I had to guess on your check engine light, it would be a bad catalytic converter or a bad 3 way coolant valve. But techstream should cough up a code