P0AA6 explanation

I use the Autel AP200. Take a look at post #37 in this thread Gen2 OBD2 app review, and also this thread
Autel Maxi AP200 - go buy this . The INF codes are in the freeze frame data for the P0AA6 code. The INF code will narrow down the area of the car that is having the problem. The Autel AP200 costs about $60 to $70 on Amazon.
Autel MaxiAP AP200 OBD2 Scanner Bluetooth Wireless OBDII Auto Diagnostic Tool with Full System Diagnostic

Base on the pictures of the battery, I would guess that the high voltage leakage is in the battery area. The INF codes would confirm that.

 

I’m currently experiencing low insulation resistance in the hv battery pack. I have taken all the modules out and tested each one and finding most with varying resistance from 500 megohms down to < 5 meg. I have tried cleaning and sanding the plastic surfaces and that initially appeared to be the fix but later on when I started assembling the pack the low insulation resistance returns. The batteries perform satisfactorily in terms of capacity and appear to have normal SOC characteristics but have low insulation resistance thus setting off P0AA6 on each trip. I checked all of my spare modules that are the same age and they exhibit similar symptoms. I have checked all of the wires, relays, and battery Ecu, all normal. I am guessing that the modules I have all have leaked some electrolyte which has left conductive paths on the module exterior.

 

So, what you are looking for is any module that has some continuity to chassis ground (ie, the battery mounting housing - frame).

What I do is to have all the modules bolted together to the frame. Then use my multimeter to check for any voltage (millivolts) between each battery terminal to the mounting frame.

If the pack is fully assembled and I have a "bad" voltage reading (more than 0.00mV), then I remove a busbar in the middle of the pack and recheck. I keep dividing and rechecking until I have narrowed it down to the individual faulty module(s).

Posted via the PriusChat mobile app.

 

Thanks for your reply

I have multiple modules that have some conductivity from the output terminal to the module exterior using my Fluke insulation resistance meter with the 500v setting. The resistance varies from a couple megohms to the maximum 550 meg ohms that the Fluke displays. I have attempted cleaning the exteriors with little success. What does help is to lightly sand the plastic housing. I suspect that over the years KOH electrolyte has seeped out from the terminals and left a conductive residue on the module exterior, especially in the area underneath the terminals down to the base surface. The modules function satisfactorily capacity wise. Currently the combined parallel insulation resistance of the modules is around 3 meg ohms which is high enough to not trigger a fault . I’m going to try doing some light sanding to the module exteriors- plastic section to remove the leakage paths, otherwise I may go ahead and replace all of them (they are 20 years old)

 

removal of busbars shouldn't be necessary. The isolation fault location is the short to the case and will be the zero reference for a voltage reading. Connect black lead of multimeter to the case and just take voltage readings, where the polarity reverses on the meter reading is where the short is located. Based on the voltage reading at that point, you can determine which module and even which cell in the module is faulted to the threaded insert.

 

You may be looking at it incorrectly. The isolation fault isn't from internal electrolyte to the plastic case, it's to the metal threaded insert on the bottom of the module. If there's a ton of seeping electrolyte, it could be from that, but normally internal microcracks where the insert was pressed into the module eventually allow electrolyte to make contact with the metal insert and therefore electrical continuity with the case. Ive seen this cured just by finding the right module, removing the fastener loosening the adjacent ones to allow a slight "pry it up" gap and slipping a piece of Scotch Super 44 between that metal insert and the case for insulation and leaving that fastener off.

 

I'm so glad I discovered this thread!

I'm helping a friend fix his 2006 Prius which was intermittently giving the red triangle.

This car has a rebuilt hybrid battery from a vendor in Florida (that's where this car came from but now it lives in Illinois). We don't know who the hybrid battery vendor or installer was, but its cover is painted bright green.

At first we diagnosed a horribly corroded voltage sensing harness and severely corroded busbars. We replaced the sensing harness and thoroughly cleaned up the orange connector on the hybrid battery ECU. Then we cleaned up the module terminals and replaced the old busbars with new nickel-plated busbars and new nickel-plated nuts. Doing this banished a large number of different hybrid battery ECU codes related to out-of-spec block voltages. I'm certain those came from the nasty voltage sensing harness.

We thought everything would turn out fine, but the P0AA6 code still comes up randomly. Not often, but it has happened more than once. I didn't know what this code indicated until I read this thread.

So now we will search for leakage current between the HV circuit and ground. I already have suitable gear to do insulation tests. I hope the cause is a module with leakage into the threaded insert where the module bolts down to the lower hybrid battery housing. I've seen old modules with crusty bits near these inserts. I've also seen tell-tale corrosion in lower housings of hybrid batteries which could only have come from electrolyte leakage near these inserts. To me these metal inserts in the modules seem to be the most likely place where electrical leakage would occur.

I'm hoping we don't find any issues with electrical leakage from downstream devices such as the inverter or AC compressor. Unfortunately my OBD device doesn't provide details about the P0AA6 code. I'll probably purchase a Priuschat -recommended OBD unit with better capabilities. From reading this thread I understand that these P0AA6 sub-codes help identify the source of the electrical leakage. I'm always improving my toolkit anyway

I'll post what we find.

 

It occurs to me that when the Prius is in the "off" state then the main contactors in the hybrid battery are both open.
In this case the + and - HV cables which go up to the front of the car are both isolated from the modules inside the hybrid battery.
Therefore an insulation tester should be able to identify whether the ground fault comes from within the hybrid battery pack itself, or from some other part of the HV circuitry. This is done by insulation testing at the contactors: First, test the battery side. Then test the "external" side.

If there is a ground fault on both sides of the main contactors then the orange cables can be detached from the hybrid battery in order to further isolate the fault.