Analysis of an 11 year old, 165K mile battery pack

Old 01-04-2019, 04:31 PM
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Default Re: Analysis of an 11 year old, 165K mile battery pack

No. It would probably help. As you warm the interior of the car, you would warm the battery faster. Personally, I would like to see a switch in the console... shouldn't be too hard. If I'm right about the method of control via shorting the PWM line, the current there is tiny, so small gauge wire would be fine.
Old 01-04-2019, 10:58 PM
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Default Re: Analysis of an 11 year old, 165K mile battery pack

Since I'm not sure if sharing the actual schematic image is allowed and I don't want this post to be deleted, I'll just share the knowledge I gained by looking at the service manual:

Battery Fan Connector (FC)
Pin # - Name - Wire Color
Pin 1 - "Not Used" - D-GN
Pin 2 - "B+" - PK/D-BU
Pin 3 - Ground - BK/YE
Pin 4 - PWM Input - D-GN/BK

BECM X2 Connector
Pin # - Name - Wire Color
Pin 2 - PWM output - D-GN/BK
Pin 3 - "Not Used" - D-GN
Pin 7 - Fan Relay Control - WH/GN

Signal Descriptions
  • The battery control module (BECM) grounds a relay to apply 12V to the fan on FC Pin 2.
    • This would need to done externally if we wanted to even command the fan to 100% all the time, not just when the BECM decides the battery pack needs to be cooled.
  • The BECM also sends a PWM signal to the fan on FC Pin 4.
    • This signal is pulled up to 5V inside the fan. The BECM grounds the line to generate a pulse width modulated signal to control the fan speed.
  • The ground wire on FC Pin 3 connects to the battery case somewhere.
  • The wire on FC Pin 1 that you would expect to be a fan speed output signal says "Not Used" both in the Fan and the BECM pins.
    • This "Not Used" may not be true because in the battery cooling system description it says "The battery vent fan motor also supplies an additional 5 volt signal that indicates vent fan speed back to the BECM, the lower the voltage the greater the fan speed."
    • The P0A81 trouble code will be set if the fan has been commanded to 35% or higher and the "Fan control signal monitor voltage to BECM is greater than 2.3 volts or less than 0.5 volt for 5 seconds."
    • The P0BC1 trouble code will be set if the "fan has transitioned from either ON to OFF or from OFF to ON" and the voltage is above 0.9V for 1 second.
Possible Control Method #1
In order to run the fans at 100% with the flick of a switch and not throw error codes, it would be necessary to come up with a circuit that disconnects the BECM PWM signal, the fan speed feedback signal, and possibly also the relay control line from the BECM.
  • The PWM signal input at the fan would have to be grounded to make it run at 100%. If the BECM monitors the PWM output, it would need to be pulled up to 5V with a resistor to make the BECM think the fan is still connected.
  • The speed signal input from the fan to the BECM would need to be simulated to make the BECM think the fan is running at the commanded speed. This may be the showstopper, unless we use a microcontroller (Arduino for example) to read the PWM signal duty cycle and feed back an appropriate fake fan speed voltage to the BECM so it will think the fan is running at the commanded speed.
    • If the fan ever had a real failure while our circuit is active, the BECM would never know. The microcontroller would also need to detect this and stop fooling the BECM when S&@t hits the fan.
  • The fan relay control signal may not need to be disconnected if the BECM does not monitor the voltage at the output. Simply connecting it to ground externally may be enough.

Possible Control Method #2
Coming someday. Need to think some more.
Old 01-05-2019, 08:06 AM
Join Date: Feb 2018
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Default Re: Analysis of an 11 year old, 165K mile battery pack

Seems simple enough to run the fan if you can get around the diagnostics tripping. Why not just have an ignition line drive a low side FET to ground the PWM signal to turn the fan on at key on.

For the diagnostic workaround and since the depth of my microprocessor knowledge stops at PIC16ís and Iíve avoided Arduinos just because I donít feel like learning something new, Iím thinking a simple solution of either using a PWM to voltage conversion circuit and an Voltage/analog to Frequency converter might work well enough. Would have to do some digging on setting up ranges of Fan RPM diagnostics compared to PWM input.

Or it literally could be a simple as taking a 3Ē computer fan that has a PWM input and tach output and tuning it so the fan spins at the expected RPM then tucking that up in the battery space somewhere to trick the computer while the squirrel cage fan runs on its own.
Old 01-30-2019, 06:41 PM
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Default Re: Analysis of an 11 year old, 165K mile battery pack

Very informative and also very depressing thread for the GM Two Mode owners. After seeing this I have lost all interest in wasting time trying to save any modules in my 10 year old + 200k miles pack. Probably not much better than the results shown by this thread. I never did like the game of wack-a-mole.
I am on the hunt for a great deal on a NEW battery for my HYHO. Got a line on one for well under dealership parts asking prices right now, just trying to verify that it has NEW modules before I complete the transaction.
Old 01-30-2019, 06:47 PM
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Default Re: Analysis of an 11 year old, 165K mile battery pack

Glad you finally made it.
Old 02-06-2019, 02:33 AM
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Default Re: Analysis of an 11 year old, 165K mile battery pack

Jaime that is fascinating data. I have ordered a replacement hybrid battery for my 09 Tahoe (it should be in this week) . After I pull the old battery (201,000 miles) and get it on ,my work bench I would be willing to gather data from the old battery and post it on the forum. You seem to have developed a good data base there.
Hate to bother but can you please provide details of exactly what equipment you used and step by step of how you went about gathering your data and applying it to the spreadsheets?
My truck actually still drives pretty good with long EV mode and autostop functioning normally EXCEPT for one incident a few weeks back where it hesitated from takeoff and had a couple of codes.That incident happened right after I had utilized the rear power supply to run an air compressor and has not happened since. The consensus here and other forums seems to be that the GM battery management uses the modules up until they are useless to recondition. I do not expect to see many use-able modules but I figured if it was not a major PITA I would try to contribute back to a great and informative forum.
If I use the same equipment or equivalent and equivalent procedures as you did, then maybe the data will actually be useful to the forum and others. All these GM Two Modes are starting to show their age and the hybrid battery packs are a major expense item for owners, so interest is only going to increase over the next few years.
Old 02-09-2019, 03:39 PM
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Default Re: Analysis of an 11 year old, 165K mile battery pack


Equipment Used:
  • Turnigy Reaktor 30A 1000W Balance Charger (Hobbyking link)
    • There are many similar chargers in the marker with an almost identical user interface. The most important aspects are that it is capable of charging 6 series NiMh cells (7.2V) at 2 Amps and discharging at 6 Amps. Many chargers can charge at 2A or more. The tricky part is finding one that can discharge at more than 0.7A like most cheap ones do. This Reaktor charger and 1 or 2 other models lower can discharge at up to 80W which when divided by the battery voltage gives you the max discharge current capability. You can use any discharge current but the lower currents will give you a higher module capacity and wont be comparable to my testing.
  • Turnigy Reaktor 350W 23A Power Supply (Hobbyking link)
    • Any 12V or higher power supply with minimum 3A current will work (Up to the max input of whatever charger you use. 36V max for the 1000W reaktor)
  • Digital Multimeter (any decent 4-digit multimeter should work, Here's the one I used)
  • 3 ft Pomona B-36-02 Banana Plug Patch Cord (
    Amazon link Amazon link
    • Ideally you would want to use the shortest, thickest possible wires to charge your modules to ensure a minimum voltage drop and power dissipation in the wires, but this is all I had so I used it. If you want to be able to compare your results to mine, I would use the same or similar 18AWG 3ft wires.
Instead of connecting the charger clamps directly to the module studs, stack 2 bus bars and put them on each end of the module with the original nut tightened to 48 inch-pounds of torque. Then clamp the charger clamps on the bus bars. Connect the banana plug wires from the clamps to the banana jacks on the charger.

Take some time to navigate the menus and get used to the key-presses necessary to do things. If you press the wrong button while charging/discharging, you'll interrupt the process and have to start all over again.
The left most button is usually to Go back or cancel a selection. The two middle buttons are usually to increase/decrease values or change menu pages. The right-most button is usually to select or start testing by holding it down.

NiMH battery Menu
NiMH DISCHARGE, 6.0A 6.00V Here is what the NiMH DISCHARGE page will look like before starting a discharge. You can set the discharge rate (6.0A) and the final voltage (6.00V) by pressing the right-most button and using the 2 middle buttons to increase/decrease the value. Then press the right-most button again to go to the next value adjustment. Once ready to start, hold down the right-most button.
NiMH CHARGE Aut, 2.0A CUR LIMIT Be sure to use the Auto charge mode and not the manual mode which is next in the menu. You can set the charge rate (2.0A) by pressing the right-most button and using the 2 middle buttons to increase/decrease the value. Once ready to start, hold down the right-most button.

The option to measure internal resistance is under the "Special Modes" menu. Hold down the right button to begin the measurement. This Internal resistance measurement does not have must meaning other than to compare each module to all the rest. Since your wiring and setup will be the same for all, if one has a very low or very high internal resistance measurement, that may tell you something about it when taking all the gathered data into account.

SETTINGS Menu <-- these options need to be set before doing any charging/discharging
NiMh Sensitivity, Delta V Default. I left the DeltaV sensitivity at 4mV which is the Default.
NiMH/NiCd Check Delay 0min I'm not too sure on what this setting does but I believe it is related to the DeltaV above. I left it at 0min.
Safety timer ON 230min Set the time limit to 230 minutes. At 6A discharge rate, it will only take a max of 1 hour to discharge a brand new module with 6Ah capacity. Obviously your old modules will take much less time to discharge. For charging at 2A, it will allow a module to charge up to 7,600 mAh which no module will ever reach unless you are doing some type of reconditioning, which i wont get into for this post.
Capacity Cut-Off ON 6000mAh I highly doubt any of your modules will ever reach this value while charging/discharging but this will be a safety cutoff.
Watt Limit (W) CHG:AUTO DCHG:80 You need to go into this menu page to verify the Discharge limit is set high enough to where it wont limit your max discharge current. I set it to the max of 80W.

Download the attached blank Excel spreadsheet. I changed the last column of the spreadsheet to add a third discharge column (second full discharge). Only 1 full discharge is necessary to know the capacity of the module, but if you have time and patience, a second full discharge will confirm the first full discharge results.
When you open your battery pack, take a permanent marker and number the modules 1 to 40 starting with the one closest to the fan.
I recommend gathering the measurements in the first two columns at the very beginning (internal resistance and initial voltage) for all the modules and then discharging/charging/discharging/charging/discharging one module at a time. If you can delay your initial measurements until 1 or 2 weeks after removing the battery from the car, that will give the worst self-discharging modules some time to discharge.
So once you have measured all the initial voltages and internal resistances, you'll begin performing the following steps for each of the 40 modules:

Initial 6A discharge to 6.0V. (Spreadsheet 1st Discharge) This will give you the capacity as removed from the car, not the FULL module capacity. The battery control module tends to keep the modules charged somewhere around 60-70% of their full capacity. Once this discharge is done, write down the mAh value given on the second line of the charger display. Wait 10 minutes before continuing to the charge step.
Auto Charge at 2A. (Spreadsheet 1st Charge) This will fully charge the module to prepare it for the next discharge. Write down the capacity (mAh value) given on the second line of the charger display in the appropriate column. This is how much power over time was input to the module. Wait 10 minutes before continuing to the next discharge step.
First Full Discharge (Spreadsheet 2nd Discharge). Same 6A to 6V as before, but you should expect to see a higher discharge capacity. This is the important measurement, so write down the capacity given on the second line of the charger display.

Now you have 2 options:
1) Repeat previous 2 steps on this same module to verify capacity and enter the charge/discharge capacities given by the charger into the spreadsheet in the 2nd Charge and 3rd Discharge column, or
2) Continue to the next module.

I did not select option #1, but did spend time trying to recondition some of the modules. If you do decide to verify the capacities, it will be beyond what I did and serve to provide better data.

To help you make a decision, calculate how long it took you to do the 2 previous steps and multiply that time by 40. Are you willing to spend that additional time overall for extra verification of capacity? if your modules are as bad as mine were, the discharge/charge process wont take very long (<1 hour). but if they take any considerable amount of charge, you will struggle to get through even the minimum first 2 steps for all the modules. Maybe you can decide on a threshold capacity that will trigger an additional verification. Like if you were to get any with over 3000mAh capacity, that might be worth verifying.
You can decrease the time required by using multiple chargers, but unless you have other uses for these chargers, you would need to buy and then sell them.

Attached Files
File Type: xls
Battery Blank Worksheet.xls (13.0 KB, 7 views)

Last edited by Jaime; 02-09-2019 at 04:35 PM.
Old 02-09-2019, 04:21 PM
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Default Re: Analysis of an 11 year old, 165K mile battery pack

That is perfect thanks. I am printing this off right now as a guide.
I might have to order the Turnigy equipment (not sure if there is anywhere here locally that sells it) so it might be next weekend when I get deep into it. I just took some basic voltage readings on the old battery to see if they were all pretty close to each other, it is penciled in on the sheet in the pic below. I know that the standing voltage data means very little but it satisfied my curiosity and helped me get familiar with the interior of the battery.
Please allow me to do my "SAFETY FIRST" Speech for anyone who is uninitiated thinking about doing battery disassembly.
A great deal of caution must be used when working on these batteries. I taped up my sockets / used electrical rated gloves / used safety glasses / long sleeved denim shirt and used general steady slow moving caution watching every move carefully. I found multiple spots around the pack where the HIGH voltage is 100% live with the busbar covers off!! These things are not play toys and are not for anyone unsure or careless. Please take this serious.

Old 02-11-2019, 06:32 PM
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Default Re: Analysis of an 11 year old, 165K mile battery pack

Gentlemen I wanted to relay to the forum an issue that popped up after my Hybrid battery replacement was completed this last Saturday afternoon. After completion and reconnecting the under-hood 12V battery I noticed that I did NOT have a time display on the head unit! Going to the menu and set clock on the basic menu it would not allow anything to be set. A little bit irritating, so of course I diod an internet search and finally figured out that there is "hidden" menu for the GM head units in these 2007 thru 2013 Tahoe/Yukon and Escalade units that allows you to reset the time. i guess the head unit has lost its time memory completely, what is really weird though is that all my radio stations were still programmed. According to what I read this loss of time can happen when the 12V battery is disconnected or becomes completely discharged. I have actually written the procedure down and put it in my glove compartment for future use, hopefully this will help someone dealing with the issue.
i could see someone driving for years without a time display thinking it could not be fixed or maybe thinking it just did not have a time display on the screen if they bought a used vehicle......................
Step 1 Punch Menu button
Step 2. Punch Display button
Step 3. Touch and hold your finger on the blank area at bottom left of touchscreen for 5 seconds. A screen with pop up to enter numbers.
Step 4. Enter code 295660 and push "Done" then the options menu should pop up.
Step 5. Go to 2nd page of the options menu (RESIST THE URGE TO PUNCH AND CHANGE ANYTHING EXCEPT FOR THE TIME SETTING LOL) punch "set time" menu on 2nd page and it will pop up a screen to enter date and time Please Note: You need to calculate your time difference from GMT the head unit uses strictly GMT and for me I had to add 6 hours to get the correct time to display. There is not a option to pick a time zone! you have to adjust your time to GMT and add or subtract hours as needed.
I really wanted to mess with some of the other settings in there but I had already read where other people had totally messed their head units up changing settings so I resisted. Time is displayed now Life is Good. .

Last edited by dnt1010; 02-12-2019 at 04:27 PM.
Old 02-11-2019, 07:25 PM
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Default Re: Analysis of an 11 year old, 165K mile battery pack

The exact same thing happened to me. The clock digits were blank and when you went into the settings menu to change it, there were no digits either. I thought a Nav software update would fix it so I bought a 2015 Map DVD on ebay. Did the update and the clock was still blank. Finally found a reference to that secret menu and was able to set the time there after a couple tries. I put local time instead of GMT, so I had to redo it. The code I used to access the secret menu was 295660.

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