P0AA6 Hybrid/EV Battery Voltage System Isolation Fault

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Dec 11, 2014
Hi fellow Focus EVers!

My 2012 FFE has given me the dreaded Stop Safely Now message and won't start. FORScan shows:

===BECM DTC P0AA6:00-C8===
Code: P0AA6 - Hybrid/EV Battery Voltage System Isolation Fault

- Previously Set DTC - Not Present at Time of Request
- Malfunction Indicator Lamp is On for this DTC
- Test not complete

among other codes.

Are there any easy diagnostic things I can do with this before I tow it to the dealer? I do have the service manual PDF. I'd like to rule out the coolant-leak issue if I can. Any advice appreciated!
2 years ago when my internal coolant leak happened at 60,000 miles, my 2012 FFE was throwing DTCs P0AA6 and P1A0A. P0AA6 is battery isolation fault, or 1 leg of the high voltage potentially conducting through the battery case via leaked coolant inside the case. P1A0A is thrown when P0AA6 is detected, so the BECM will request to shut down the car.

If you have Forscan and a laptop/computer (if you don't, get the one with the USB connection), you can reset the DTCs to drive the car around, but depending on the severity, it may still throw you back into a SSN after a few miles (Mines would let drive as long as I didn't cut the car off and back on. Then I would have to clear the DTCs to drive again :lol:). A temporary fix is to do is doing the coolant bypass. Looking at how others have done it on the Facebook group, you can probably get it done without having to remove the upper pack.

- Disconnect the upper pack high high voltage safety disconnect. Wait at least 5 minutes before working on the pack.

-"vacuum" the coolant out the lines from the main inlet/outlet going into the pack. There is a post on the Facebook group where someone has done this.

-remove the lid of the upper pack and carefully vacuum and wipe out any visible coolant. You'll probably have coolant piled near your precharge circuit, which could've triggered the code. Be mindful of anything orange and use plastic tools or tools wrapped with electrical tape if
possible. In picture, just screws circled in green need to be removed.

-Pull drain plugs on the bottom of the upper battery pack, as you have modules that sit directly under the upper pack.

-Make a bypass loop for the upper hoses going to the coolant lines. You just need some clamps from an auto parts store to fit the hose and a plastic housing piece that can connect the inlet hose and outlet hose together, probably from home depot or lowes. Ask on the Facebook group for photos of people who have done the coolant bypass, some of their loops are done much neater than mine is.

-Let the lid stay off for a bit to dry things off (bus bars and case should be dry, especially check the bus bar going to contactors. I think there is a current sensor on one of the contactors bus bars). If you're feeling daring, after it dries, clear the SSN related DTCs with Forscan, leave the upper pack's lid off, and take the car for a little drive not to far (around your neighborhood). Keep your Laptop and Forscan with you, just incase (you'll notice the car is a little quicker, too!)

Doing the bypass should cost you under $50, the most expensive thing you'll get is 1 or two things of antifreeze.
I also have the 2 post on here from when I did the coolant bypass, if that helps:

(removing the pack, although you can probably get away without having to do that. You should remove the rear seats though) http://www.myfocuselectric.com/forum/viewtopic.php?t=4966

(tearing the pack apart and removing anything related to upper pack cooling, along with doing the coolant bypass)
P0AA6 occurred to my 2014 FFE. This occurred after I removed the rear disconnect cover with an 8mm bolt. The orange cover has two pins that is probably part of the HVIL (12V loop part). After I placed the cover back on, a yellow wrench occurred with P0AA6 using Forscan. Went to dealer, they confirmed P0AA6 and recommend full HVB wiring harness replacement for $3,500. I declined.

Why does simply removing the cover cause the P0AA6 code? Could the connection be loose not allowing the code to resolve and clear?
Trinhray said:
P0AA6 occurred to my 2014 FFE. This occurred after I removed the rear disconnect cover with an 8mm bolt. The orange cover has two pins that is probably part of the HVIL (12V loop part). After I placed the cover back on, a yellow wrench occurred with P0AA6 using Forscan. Went to dealer, they confirmed P0AA6 and recommend full HVB wiring harness replacement for $3,500. I declined.

Why does simply removing the cover cause the P0AA6 code? Could the connection be loose not allowing the code to resolve and clear?

Could you provide a photo of the cover you are speaking about?
The Orange interlock behind the rear seats does have an HVIL connection. If you were to remove the interlock while there is HV being used, you are going to get warnings and such. It is best to power down the vehicle, disconnect the 12V battery, and then remove the interlock. Also, if there is sufficient current running through the HV system when the interlock is removed, you are going to get some arching. That ain't good. Sure, the HVIL is supposed to shut down HV, but how fast will the contactors react as compared to removing the interlock?
Thanks Heima.

The P0AA6 (yellow wrench) was triggered with the car powered down but not 12v battery disconnected. The orange cover in my previous post was for the large disconnect with two small pins (12v HVIL?). This is to the right of the Interlock fuse. Skyguy provided a picture of the upper battery pack earlier, its the one with the red arrow. For some reason, the dealer could not clear this code and recommended a harness replacement for $3,500. Maybe keeping the 12V battery connected and removing this cover with the two pins triggered a fault that cannot be cleared? This code does allow continual driving so kind of a nuisance at the moment.

The P0A0A was triggered when the interlock fuse is removed. The dealer was able to clear this code. I tried using Forscan (extended license and OBDLinkEx) but it could not clear or reset. This results in Stop Safely Now warning and car is immobilized, hence required tow back to dealer.

Intent: I would like to modify my FFE with additional batteries for longer range but currently bogged down with fault codes. I check the Forscan forums but did not see much relevance to FFEs.
Thank you Trinhray, do you have the service manual? If not, you can get it here:

I checked all of the tests for P0AA6, and they were for isolation. The checks are made at the connector terminals for it seems all battery pack HV connectors. So maybe by opening up that connector moist air got into the pack, and that is creating an isolation fault. Possible, but highly unlikely.You could measure at that connector as described in the service manual, and see if it is at spec. If not then maybe something happened to the connector on the inside.

I do not believe it is an HVIL problem, because the service manual does not describe checking any HVIL connectors.

Sorry I could not be of more help.
I'm working out some battery issues of my own right now but hopefully I'm getting close. Some things were mentioned here that don't quite jive with my recent experience. I'm not saying what is right or wrong, but I'll give you what I think to be true...at least for me.
- P0A0A is an interlock error. I got this error after fixing my P0AA0, P0AA1, P0A95 errors. These are, by the way, contactor issues and I've replaced the offending contactor and these errors have gone away...leaving me with P0A0A.
-The interlock is those 2 little pins on the service disconnect / fuse. There is one on every High power connector. There is another one of these interlocks on the connector adjacent to the removable disconnect behind the back seat. There is another by the passenger side rear wheel, and another on the driver side rear wheel, and under the car just in front of the lower battery.
-Be very careful with the last 2 connectors I mentioned above. They are brittle and I've found that the Ford Dealer's service department broke both of them attempting to diagnose my issue....which is why I now have the P0A0A:00-8B error.
-To help verify my issue, I pulled the service disconnect and tried to start the car and I see no additional error....just the P0A0A:00-8B.
-Lastly, I'm not done attempting to fix this mess, but when I do get it all fixed, I'll post a write up here.
-This error is reported by the BECM

There is another interlock at the front of the car between the TCM and DC to DC and some other components, but I don't think these would be the same reporting module as the issue above.
I've seen it mentioned before that there's a process to bypass the HVIL checks - that is, ignore that fault when it occurs. I doubt it's persistent, but that might be worth doing while troubleshooting.
Sorry I didn't post a reply. I do have the car working now for several weeks now. All is good. So yeah, it was the interlock issue, but not with the service disconnects. It was the HV connector at the driver's side rear wheel. Basically, the Ford Service people totally destroyed that connector. Not only was the clamping latch busted, but the 2 tabs on both sides of the connector on the battery pack were busted off. That's what the mating connector interfaces with to clamp the connection down. So when I just pushed the connector on all the way, the car would go into drive.

So with all that figured out, I buttoned everything back together and started testing it. No issues. So I started driving it to work and back...about 10 miles each way...no issue driving, but everytime I finish driving or before driving again, I reach under and push the connector to ensure it is fully seated. On 2 occasions, it had wiggled out a little as I could feel the movement on the connector when I pushed down on it.

If it were just the latch on the connector on the end of the high voltage cable, that could be replaced...but the one on the battery also needed replacement. So what I did was to make two metal (stainless steel) brackets that uses the same screw holes that secure the connector to the battery. With those in place on each side of the connector, I ran a nylon wire tie between them to secure hold the connector in place. It has been holding tightly for that last few weeks. So now I just need to check it every couple of months to make sure everything is still firm and snug. So far so good.

I have a writeup with pictures over on the facebook forum along with another write up on replacing the contactor. It is worth signing up for that facebook group if you ever need help with anything.
Thanks. I just couldn't come to terms with letting the car go or paying $14,000 for a battery swap. The thing I found odd about the contactor is that Ford does have the pack of contactors in the upper battery available for $900. It is odd because it seems the Ford techs don't go inside the battery even though the error code said exactly what the error was...positive contactor stuck closed. Anyway, glad they didn't because now I know even more about the car to do the work myself. As for the broken HV connector, that's just disappointing...but I had a friend with some extra sheets of stainless steel so I made a couple of brackets out of it. I'm happy with the result as it doesn't put any additional stress on the plastic connectors which seem to be a little brittle. Anyway, good luck with your vehicles. I hope to get a few more years out of mine...at least.