2008 Prius. I've had it for nearly 3 years and it drives beautifully as my daily driver. It has a NexPower Sodium V3 battery in it (the two-pack system, not the regular blade-style), which was a replacement of the V2 NexPower Lithium that failed. I drove it Monday and Tuesday, then stayed home Wednesday, then it threw P0AFA on Thursday. The car turns on fully and the ICE stays running. The LCD states "Problem" and the RTOD, VSC, and (!) dash warning lights are on. Car shifts into all gears fine and drives but the ICE stays on. Battery voltage on block 1 and block 14 fluctuates from positive to negative every few seconds. I checked the 12v battery and also tried clearing codes and it came back. Today I took the battery compartment apart and checked all the terminals and connections, as well as to the ECU. No corrosion anywhere. The two main nuts connecting the bus bars back to the cutoff seemed to be a little loose when I took them off but I tightened them back fully. After putting it partially back together I started it up again and P0AFA came back. I'm wondering if it's the battery ECU? All help is greatly appreciated. Thanks!
A negative voltage for a hybrid battery block indicates a problem with the voltage sensing wires somewhere or a problem with the battery ECU. It could be a wire issue at the battery end, at the battery ECU end, or somewhere between.
Thank you, Brian. First I tested the voltage at the main connection into the ECU and it was good, then checked between the pins and found an inconsistency between the red and black wires. So I took the whole battery assembly out and took apart the two sodium battery modules. I traced and tested all of the balance leads between the cells and the battery control board. When I located which module the issue was in I then tested the individual leads thinking there was a loose connection on the battery. All of those tests came back normally. I then did the same with the second module. Again, all good. I re-tested some of the leads and then thought to check the connectors to the board itself - Voila - an issue! It turns out that one of the leads on the bottom side of the first battery module had short-circuited and blown. See black marks in photos. In Jack's reply to my previous email he mentioned that this was identified as a failure point in some cases of the 2-pack sodium style and was a contributing factor to them discontinuing the 2-pack module. I emailed Jack with an update and asked if they had any of these control boards leftover. He replied within minutes and said Yes, they do, and that he would send it to me. Soon after I received a shipment notification! I should be able to install it Wednesday or Thursday and will know if this solved the problem. Since everything else tested good and this is definitely bad I believe (and HOPE) and that this will solve my problem. Interesting side note: When I took the battery assembly cover off I noticed that the batteries were covered in light droplets of condensation. Jack had mentioned that this happens on some models and that the short on the board is related to the condensation. I'm not really sure why, but thought I would mention it here for anyone else who might run across the problem.
