Need advice '02 battery issue 144K miles

Check the voltage on your 12V battery. This has been know to cause all kinds of electrical things to happen when it gets weak.
TomK

 

That sounds like the rebalancing cycle that the computer occasionally runs in order to keep the battery in the best condition possible. I've noticed it in my car a few times (I've had the car about 6 years). Basically, instead of aiming to keep the battery around 60% as it normally does, it will go into a mode where it steadily charges all the way up to 100%, stays there for some minutes, and then returns to usual behavior and lets the state of charge return to around the usual 60%. The first time it happened in my car I sort of panicked, turned it off and on and such, trying to intervene, and the time after that I just thought "I'll watch this and see what it does," and that's what it does.

The fact that it ran the cycle at all means your battery is not brand new and perfect. But you weren't expecting a 12 year old, 144k mile battery to be brand new and perfect. By running this cycle on it now and then, the computer is working to stretch its life out as long as it can.

-Chap

 

Chap,

Do you know if the Gen II and Gen III do this as well?

 

Chap that is so cool if the computer actually does this. I want mine to do this as I have almost had it a year and know nothing of it's history but I have to assume it is an all original battery.
TomK

 

I concur with Chap. I have observed this in my 01 at least 3 times before it got runned over by a reindeer.

 

You might consider getting a Prius-aware scanner and taking a look at your 19 module-pairs. Also, take a look at the four temperature values to see if there is a pattern.

Right now, I wouldn't set my hair on fire.

Bob Wilson

 

Mini VCI from Amazon.com will set you back around $25. This will provide you with almost the same diagnostic capability as the Toyota dealer techs.

You need a Windows XP or Windows 7, 32 bit OS laptop to run that.

 

To my untrained eye, the battery voltages after start and running look pretty good and are relatively consistent. I don't think there's much of an issue at this time unless a discharge test would reveal a low module. I'll let someone better equipped answer that question.

 

First Snapshot

• 14.85V Min Voltage
• 15.34V Max Voltage
• 15.34 - 14.85 = 0.49V > 0.3V threshold to set unbalanced code
• #11 Min voltage block

Second Snapshot

• 16.07V Min Voltage
• 16.34V Max Voltage
• 16.34 - 16.07 = 0.27V ~= 0.3V threshold to set unbalanced code
• #9 Min voltage block

This is a marginal battery pack because the lowest module pair and highest module pair differ by 0.27-0.49V which is close and above the 0.3V threshold needed to throw a code from an unbalanced pack. The weakest modules are in the middle which matches past experience. But the pack temperature also shows a problem:

1. 61F, 57F, 57F, 61F - starts
2. 70F, 64F, 64F, 66F - ending, #1 probe is significantly hotter! Smoking gun.

A failing module runs hot and the first clue is excessive heat. It is getting hot in one area, group #1.

Mitigations:

• Manually restack or balance the pack - Autoline Daily reports someone does this commercially. However, I would do it manually by ordering 38 module voltages, parallel wiring and charging to 8V, and restack pairing strongest and weakest modules with weakest module pairs on the coolest ends and no weak modules adjacent to each other. Start your battery replacement fund.
• Buy a rebuilt pack from a quality rebuilder - they have the tools, inventory, and knowledge to build a quality pack and comes with a guarantee. It will have better modules.
• Buy a pack from Toyota - a known quantity, it will have the same version of modules that just ran a decade. Bring a little more money but easier and faster.

Bob Wilson

 

Volume 1, the diagnostic manual, describes a controlled test that does a controlled discharge using "R" and a curb and then uses "P" or "D" to put a charge back on while monitoring the traction battery. The tech service can provide the specifics. You might look for a used manual set on eBay.

Rebalancing a 38 module battery pack means equal charge them and using a controlled load on each to rank them. Then parallel charge them and restock the pairs. But this is just buying time. Battery modules age, some faster than others.

The diagnostic codes are set but the full specifications are not documented. So time and temperatures may be involved but not documented in the manual. I could speculate if I were in a bar about why there is no code but the diagnostic manual has a definitive test.

Bob Wilson

 

Ok, I'm posting from a bar so I can speculate.

Measuring module-pair voltages in a running Prius has some challenges:

• Current range: -50A to +70A
• Voltage measured by sequential sample held in a cap and read
• Noisy MG1 and MG2

In an environment like this, I would toss out readings where the current changed too much . . . If the current sign changed, useless. Now there algorithms that could smooth the data but I am at a bar.

So let me once again endorse the diagnostic manual test.

Bob Wilson