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.
