I took some voltage readings from the 20 battery module pairs in the battery pack to confirm that the battery pack is bad.

It started out at 41% state of charge and the Tahoe did not go into Auto-Stop mode until it reached 72% state of charge. I revved the engine during the charging as you can see by the voltage spikes as the State of charge rises. Once the Tahoe went to electric only at 72% SOC, I drove it slowly up a long, slightly uphill, driveway. Then the gas motor turned on and I put the gas pedal to further down to use the electric power assist during acceleration.

How does it look to you? The largest voltage difference between the minimum and maximum module pair voltages was 3 volts at one point. Does this confirm a bad battery?

 

I don't have GM specific experience, but given that the pack is manufactured by Toyota, and it uses the same internals and the same voltage monitoring methods and presumably at least a variation on the same battery management as every other NiMH-based hybrid, I would conclude an absolute yes, your battery is bad.

Generally speaking, even under heavy currents, the deltaV between min and max is typically less than 0.6V. Under low currents, <20A, less than 0.3V, and at rest, < 0.2V but tpyically less than 0.1V for a truly healthy battery.

Do you have current data, and can you provide access to the raw numbers?

 

I included 2 current parameters in the measurements but one of them "GM.BATTERY.CALC_CURRENT" looks bogus due to insanely high numbers during some part of the scan. I also took measurements from a "GM.BATTERY.CURRENT_SENSOR_V" which is a DC voltage centered around 2.5V which goes up or down slightly depending on charging/discharging. Do not know if that is meaningful data. I am unable to rerun the test at the moment with different parameters since the Tahoe is currently 500 miles away.

I included the CSV file generated by ScanXL.

Thanks.

 

The 3 volt delta is not good. It should be down where S Keith said

 

In short, if that voltage data is correct, your pack is bad or severely imbalanced.


Generally speaking, that's one of the messiest group of block voltages I've ever seen, and I've seen some **** shows, which kinda brings the data into question.


Block 1 swings from the minimum to the maximum by a large degree.... almost certainly a sign of a failed cell.


Near constant voltage with climbing SoC from 45-60 is weird.


Voltages plummeting to the 11-12V range with deltaV exceeding 2V and small drops in SoC is very irregular.


Causes:
Bad battery.
Sensing issue (block voltage harness)
Bad data.

 

I took some more data today. This time I used Torque Pro on a tablet instead of ScanXL.
I am not 100% sure about the battery current equation I used since the one I had found online was not correct (was giving obviously bogus data with current values over 3000A) and I modified it. I ended up with current values that seem more reasonable.
The attached line chart only shows data from Rows 1324 to 2017.
Also, I don't know if it was a coincidence, but as I was capturing the data, the check Engine light turned on and the P0BBD DTC was recorded.
P0BBD = "Hybrid battery pack voltage variation exceeded limit"

 

Again, if your data is good, your battery is bad.

The code would seem to confirm it. There is no reason to think it's a coincidence.
ALL data presented thus far says your battery is bad.

FWIW, it's the worst battery I've ever seen - by an almost unbelievable amount, which keeps bringing me back to the accuracy of the data.

It's like this.... There's like a big bucket of bad batteries. The best of them settle on top with the worst on the bottom. Yours is in the outhouse under a weeks worth of excrement.

It's so bad, I find it hard to believe that the battery management system would even utilize it to any significant degree. If that Toyota battery were in a Toyota car, it would essentially be disabled, and you'd be in permanent limp mode if the car would start at all.

All of the above again leads me to question the accuracy of the data. Additionally, I see a current value of 211A. I'm pretty sure that's not possible.

Concerning the chart:

When you look at 0.5V spaced gridlines for the Y axis, it's pretty rare that they stay within that range even with very low current.

At the beginning of the chart, there is basically a 2.5V delta with almost no current - that's stupefyingly terribad of epic proportions.

You either have bad data or a battery that is so much worse than the worst I've ever seen, it's likely the worst one on the planet. Well, the 2nd worse. I actually have a Gen1 Prius battery that holds that title - the victim of a mechanic thinking he could "shock" the battery back to life with his welder.

 

P0BBD = Bad Battery. It will not get better on its own.

 

How did you record the voltage data from your battery pack? I think my battery is bad, today I was driving down the freeway and the car shut down and got codes:
P0BBD = "Hybrid battery pack voltage variation exceeded limit"
P0AC4 = "Hybrid Powertrain Control Module Requested MIL Illumination"
P0C01 = "Hybrid battery pack voltage variation exceeded limit"

I let it sit for a while and got it to start eventually. I have been generally getting 17-18 mpg average which I feel is lower than it should be.

Any help would be great!

 

I have a bluetooth OBDLinkMX device that I plug into the OBD2 port and I used software called ScanXL on my PC and the Torque app on Android to get the voltages.
In Torque you can request the following PIDs:
Battery Module#, PID
1, 2240E4
2, 2240E5
3, 2240E6
4, 22410B
5, 22410C
6, 22410D
7, 2240F0
8, 2240F1
9, 2240F2
10, 2240F3
11, 2240F4
12, 2240F5
13, 2240F6
14, 2240F7
15, 2240F8
16, 2240F9
17, 2240FA
18, 2240FB
19, 2240FC
20, 2240FD
Divide the returned value of each by 10 to get the voltage. The formula you enter in Torque is "A/10" for the voltages.


The State of charge is at PID 222411. The formula is "(A*100/255)"


The battery pack current PID is 2240D2. The formula I used is "((signed(A)*256)+B)/20)". I'm not 100% sure this is accurate but it shows you when it is charging and discharging which matches when the voltages go up and down.