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P0AA6 Hybrid/EV Battery Voltage System Isolation Fault

Posted: Fri Jun 17, 2022 5:00 am
by MarkTurner
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!

Re: P0AA6 Hybrid/EV Battery Voltage System Isolation Fault

Posted: Fri Jun 17, 2022 6:38 am
by skyguy_6153
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.

Re: P0AA6 Hybrid/EV Battery Voltage System Isolation Fault

Posted: Fri Jun 17, 2022 6:45 am
by skyguy_6153
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) viewtopic.php?t=4966

(tearing the pack apart and removing anything related to upper pack cooling, along with doing the coolant bypass)