@S Keith Hi guys,

Background: 2007 FEH, 100k miles, no codes or known issues. I wanted another year of reliable service so I had the 100k mile inspection/service performed and replaced the battery with a remanufactured one from GreenTec Auto. The new battery seemed to resolve all my complaints about the old battery, regenerative braking was back strong, battery would charge to 60% SoC on long downhills just like new, and mileage jumped 5mpg. I thought all was well.

The Problem: After a week or so of carefree driving I experienced the HV battery discharging from 52% down to 29% after sitting overnight, which is exactly what the old battery did.
I've confirmed the discharge still occurs after 12h to 72h of sitting, 12v battery fully charged, nothing connected to OBDII port, all doors closed, no accessories left on. The fact that this happens on both batteries makes me think the problem is in the vehicle not self-discharge of the HV battery.

Experiment: I parked in the garage at 42% SoC and pulled the HV Service disconnect plug so the HV battery is isolated from the vehicle. Going to let it sit for a day or two and check SoC, should be unchanged.

I'd appreciate any thoughts on what's happening here and what else I can try to diagnose or fix this issue. Tnx

 

If it passes the test, maybe it's time to start pulling off relays and fuses in a targeted fashion.

 

The service plug alone does not isolate the battery. It just breaks the series circuit. The sense wires are still connected, and they're the ones that drain it in long term storage.

In addition to the service plug, remove the harness on the Driver's side with a 10mm socket. THAT will isolate the battery.

Consider that SoC isn't fixed. It's mushy. Big changes in temperature force a recalculation of SoC until the BCM can assess the voltage response to current at a given temperature.

 

How accurate is the PID that shows current in/outflow for diagnosing drain?

 

The PID is presumed accurate; however, in the context of this issue, using that feature would contribute to drain.

 

Thanks for the ideas guys.

Steve, I understand that SoC can be mushy, but I hear the engine and MG laboring to recharge the battery following the low SoC events.
Also following low SoC the Scangauge has to be commanded ON with a button push, with normal SoC the SG comes on when the key is turned, don't know what that indicates but it is consistent behavior, possibly low voltage on OBDII.

Have you ever encountered this problem before and been able to find the cause?
Appreciate any troubleshooting ideas if you have them, on the assumption problem is in the vehicle not the HV batteries.

 

Check all normal parasitic draw stuff, it's a common problem for cars in general. I just looked on youtube and there is tons of stuff:
GreenTec is shady but sounds like you got an ok battery from them so it must be some other circuit in the car that has an issue.

 

Low OBDII voltage is the 12V. Have you load tested the 12V?

 

I had the battery load tested today, tested good.

The Scangauge not turning ON with the ignition key has been a reliable predictor of low SoC, even though the underhood battery is at 12.7v. I don't understand that either.

I'm continuing to see occasional overnight discharges to exactly 29%, never higher or lower. Otherwise all performance is normal and much improved over the original HV battery.
My only option seems to be driving it until I get a hard failure or a code that provides a clue to the problem. I have a 2k mile road trip coming up, so if I make that successfully then I'll have the time to work on this some more.

 

Did something ever break when you had your original battery? And did it discharge when you isolated the traction battery? I don't think you're going to have a hard failure. Have to find the parasitic drain or it will keep happening.