UPDATED! Repaired Prius traction battery ; Warning lights

Hello PriusChat!

Background:

I recently bought a Gen2 Prius with high mileage for a fuel-efficient commute car.

A bit after buying the car, I received the Red Triangle, Hybrid Warning System, VSC, Brake Warning lights. The car still drove fine. Toyota checked the codes and determined hybrid battery failure. Being out of warrantly, they quoted me $3600.

Being a DIYer, I removed the traction battery and checked the modules. Most modules sat around 7.43V, but two of them were between 6.5-7V, and a four were only slightly low, ~7.20V. I purchased six modules from ebay to replace the low modules, as well as two HiTEC 4x chargers. I performed the discharge > charge cycling as described in a few threads here on this site, and made sure to wire the modules up in parallel at the end to equalize the voltages.

The result was that all modules had ~5000 discharge capacity, and a final voltage of 7.82-7.83. I put the traction battery back in the vehicle yesterday (left the seat off until I was certain I wouldn't be pulling anything out), and hooked everything back up. There were no warning lights when I started the car up to test.

The Issue:

Today, I test drove it for roughly 12 miles, and the Red Triangle/VSC/Brake/Hybrid Warning appeared as I was braking while exiting the interstate.

What I have checked:

12V Battery has 12.62V cold; 12.24 with lights/radio (start 1x with no brake), 12.15 in ready (start 2x with no brake), 13.93 fully started and ready to drive.

Inverter pump reservoir appears to have pretty good flow, and I can feel vibration when I touch the inlet hose.

Gas mileage during my short trip was 46mpg, with a mix of city and highway.

The car appears to drive perfectly fine.





In which direction should I proceed from here? What else should I check? Thanks for any input!

 

So I took the car to work today, which is a roughly nine mile trip.

The Master Warning light and the Hybrid Warning light remained lit the entire time, but the Brake/VSC lights did not appear. The drive went smoothly. The battery stayed between 4 and 6 bars for the entire trip, but it is a pretty hilly trip. The battery didn't appear to charge or discharge especially quickly.



I did perform a 12v battery check using the Maintenance Mode (MFD info button, turn on/off lights 3x), and here are the results I saw:

12v Maint mode, resting = 12.1 to 12.2v
12v Maint mode, car in ACC mode = 11.9v
12v Maint mode, car started = 14.1v

The guide on this site suggests that a resting voltage of 12.4-12.8v is appropriate, and an ACC mode voltage of >12v. My 12v battery is obviously showing a bit lower than this. Based on this, I will probably purchase a new battery as a precaution.


Any other leads? What else should I check? Thanks for any input!

Edit: I would like to note that I also removed all the corrosion on the buss bar copper terminals, and cleaned the battery vent fan before reassembly.

 

Quick update

I drove the Prius to the store today. NO Hybrid Warning Light, YES VSC/Brake/Master Triangle. Halfway there, the check engine light popped also. On the way back, the Hybrid Warning light DID pop, as well as the Master Triangle/VSC/Brake/CheckEngine.

I am noticing that all of these lights just come and go pretty randomly. If the problem were the Hybrid system, I would expect the light to always be on. Similarly, if it were the VSC/Brake I would expect all those lights to be on always.



I am really questioning whether this is a 12v battery issue, I have heard a failing 12v can produce some very wacky error codes.

I will update again if anything new happens.

 

Hehe, perhaps.

I am going to be placing an order for a Mini-VCI tomorrow morning, hopefully I can get it here this week to diagnose.

 

Once I get my Mini-VCI in, I will monitor the voltages with it. I don't particularly feel like ripping apart my HV battery again to test the modules, but I will if I must. I have been a bit suspicious about this, as I had a DOA cell in the batch I bought off of ebay; another one of those cells may have been pre-failure. However, the battery has been performing admirably since the discharge>charge cycling.

Definitely going to get techstream soon. Thanks for the suggestion, if I end up cracking my battery open again I will do this.

 

When doing the discharge>charge cycling, the module produced a maximum of ~1100 discharge capacity. After 3 cycles, it was still around ~1100. Seems like a module requires >3000mAh to properly function. I measured the voltage, and measured again about a day later. Original voltage was ~7.8, second check was ~6.4v. I have heard they lose a bit of charge after sitting, but certainly not that much.

I soaked the busbars and the nuts in vinegar and scrubbed with a wire brush to knock any corrosion off. I didn't use a torque wrench to tighten the nuts back, but they were plenty tight. The module studs looked pretty clean, not a lot of corrosion there. I am going to purchase a Mini-VCI and check the codes before I crack the battery pack open. I don't want to do all that work unnecessarily.

Thanks for the suggestion.

 

Well, starting yesterday I noticed that the ICE was spending more time than normal to charge the HV, even though the HV was at 5-6 bars. I also noticed that during braking, I wasn't getting the normal "99.9mpg", but instead ~65mpg. The same intermittent light issue.

Today, while traveling I heard the HV battery "tick" while driving and the car popped into limp mode. Turning the car off and on allowed me to drive with battery a bit more, but the ICE was spending 100% of the time charging the battery, which according to the MFD, stopped accepting a charge altogether. It got down to 1 bar and ticked off again, and I got myself home in limp.

I guess I will pop the battery out again and check the voltages of the cells. I already received 1 bad cell from an ebay seller, I am wondering if more cells from his shipment ended up failing as well. My Mini-VCI is due to arrive sometime in September.

I am thinking that the lessened mpg while braking is due to built-up resistance in the HV pack. Hopefully, if I can figure out which modules need a replace, I can get it back on the road soon. I bought a couple spares in case of something like this.

 

Pulled the battery apart and re-checked the voltages of all the modules. Here's my data. Values are in volts. Modules with a (*) are ones that I just replaced in my recent battery repair.

1 - 7.73
2 - 7.75
3 - 7.73
4 - 7.77
5 - 7.74
6 - 7.74
7 - 7.74
8 - 7.72
9 - 7.78 (*)
10 - 7.75
11 - 7.77
12 - 7.72
13 - 7.78
14 - 7.75
15 - 7.79-7.80 (*)
16 - 7.77
17 - 7.73
18 - 7.76
19 - 7.70
20 - 7.78 (*)
21 - 7.74
22 - 7.78 (*)
23 - 7.74
24 - 7.81 (*)
25 - 7.77-7.78 (*)
26 - 7.75
27 - 7.79
28 - 7.75

Module 19 looks possibly suspect. I will probably run a single discharge>charge cycle through each cell, hopefully that will show if one of the modules has suddenly lost the ability to charge/discharge.

I have a Mini-VCI arriving sometime in September, that will allow me to get some better diagnostics

 

Best way to load test the modules? Car headlight with some wires soldered on, with alligator clips at the end?

I was under the impression that Autozone wouldn't have the appropriate "Prius-aware" code readers. I have an Advanced Auto pretty close to my house, I might try to hoof it down there, if indeed they would have something to read my codes.