[Niko]

Since November, our C-Max Energi has been experiencing sporadic errors and the following is displayed when reading out the error codes:

P0AA6
Raw code: 0AA6
ECU: 7EC
Status:
Steht aus
OBDII: Hybrid battery voltage system - isolation fault


There must be an insulation fault somewhere in the HV system. Ford Germany no longer does service for this car (too less sold), so now I have to look for the fault myself. Can anyone help me with the following questions:
Does anyone know this fault?
Where could be most likely the insulation fault? Plug connectors, modules, or HV-battery.
Where can I get a circuit diagram?

It is strange that the error only occurs when the battery is charged. As long as one drives only in the hybrid mode the error does not occur.

 

[ramsin.ishaq]

I too have been getting this code intermittently for the past couple years on my 2017 C-Max Energi, and have made a few trips to the Ford dealership to service this with no success, it seems to always come back.

For me it happened in all 3 modes, and tended to happen more at higher speeds when the gas engine was being stressed (30 min. drive). I think in my specific case the reason for this fault is moisture/humidity related.

I barely use my air conditioning system in my car, which means the battery system is constantly struggling with dry or humid air. For the past few weeks I have been using the Max Defrost setting with AC and warming my engine up for a good 15 minutes like the manual suggests for cold weather operation. I think the heated cabin air is also giving the battery a more optimal environment. The two vents in the trunk along the windows on either side feed the battery with the airflow it needs, so the cabin air is also being used to warm or cool the massive battery pack in the trunk also.

I'm not that knowledgeable with electronics but as far as I know in dry weather I seem more prone to getting static shocks and also humid weather can cause condensation and I think both extremes can create a condition where static electricity builds up or discharges, which in the case of the vehicle may be triggering the sensor to display a code indicating an isolation fault.

Tl;Dr: try using Max defrost with AC on or cooling with Max AC in hot weather to provide the optimal temperature and humidity levels to the cabin air-vented battery in the trunk and prevent possible electrostatic anomalies causing the code. After wasting money on repairs that don't solve the problem, this is what I've narrowed it down to.

 

[Niko]

I too have been getting this code intermittently for the past couple years on my 2017 C-Max Energi, and have made a few trips to the Ford dealership to service this with no success, it seems to always come back.

For me it happened in all 3 modes, and tended to happen more at higher speeds when the gas engine was being stressed (30 min. drive). I think in my specific case the reason for this fault is moisture/humidity related.

I barely use my air conditioning system in my car, which means the battery system is constantly struggling with dry or humid air. For the past few weeks I have been using the Max Defrost setting with AC and warming my engine up for a good 15 minutes like the manual suggests for cold weather operation. I think the heated cabin air is also giving the battery a more optimal environment. The two vents in the trunk along the windows on either side feed the battery with the airflow it needs, so the cabin air is also being used to warm or cool the massive battery pack in the trunk also.

I'm not that knowledgeable with electronics but as far as I know in dry weather I seem more prone to getting static shocks and also humid weather can cause condensation and I think both extremes can create a condition where static electricity builds up or discharges, which in the case of the vehicle may be triggering the sensor to display a code indicating an isolation fault.

Tl;Dr: try using Max defrost with AC on or cooling with Max AC in hot weather to provide the optimal temperature and humidity levels to the cabin air-vented battery in the trunk and prevent possible electrostatic anomalies causing the code. After wasting money on repairs that don't solve the problem, this is what I've narrowed it down to.

Hi Ramsin,

Thank you for your comment.
You are right, the error depends on the weather. We had a lot of rain in the winter time. Since the error occurred nearly every second trip. For two weeks it is now dry and has not been raining at all. The outside temperature is colder than in recent months, at night is still frost. Since last Monday, the error no longer occurs. It was the same last summer, everything was fine until November. My guess is that water is getting in somewhere, maybe in a connector that is not properly protected from the humidity. I am an electrical engineer and can therefore understand the matter.
It's a big mess that Ford doesn't repair the vehicles here in Germany anymore and the service centers don't get any documentation. If I could only somehow get circuit documents where I can see which plugs are where, then I'm already a bit further.

Have a nice day

 

[ramsin.ishaq]

Hi Ramsin,

Thank you for your comment.
You are right, the error depends on the weather. We had a lot of rain in the winter time. Since the error occurred nearly every second trip. For two weeks it is now dry and has not been raining at all. The outside temperature is colder than in recent months, at night is still frost. Since last Monday, the error no longer occurs. It was the same last summer, everything was fine until November. My guess is that water is getting in somewhere, maybe in a connector that is not properly protected from the humidity. I am an electrical engineer and can therefore understand the matter.
It's a big mess that Ford doesn't repair the vehicles here in Germany anymore and the service centers don't get any documentation. If I could only somehow get circuit documents where I can see which plugs are where, then I'm already a bit further.

Have a nice day

Thank you, I'm glad you're able to confirm that through your expertise. I may not have experienced this problem for the first few years of owning the car because with the My Ford Mobile app I was warming my car up for 15 minutes almost every morning while plugged in.

Now that I think of it the recurring isolation problem seems to have started around the same time I stopped using the preheat feature from the app first thing in the morning.

If I were to find some damage on the wire protector do you think that some rubberized flex and seal tape would be a good enough fix?

 

[Niko]

Hi Ransin,
I have to wait until it gets warmer outside then I can start looking for the error. Now it is still too cold in our country because I have no heating in the garage and it is also very small.
Can you find an emal address of the technical support of Ford in your area. I will try to get there schematics where I can see where connectors are which are related to the battery.
I promise to inform you when I find the cause.

Have a nice day

 

[nipponenergy]

Hybrid Battery Voltage System Isolation Fault is what the problem code P0AA6 stands for. The low voltage system and the vehicle's frame are kept apart from the high voltage system. The code P0AA6 will be set if there is a lot of voltage on the low voltage side. It could malfunction for the system with high voltage.