High Voltage Isolation Failure?

[ElectrifyAllTheThings]

I bought a 2017 Ford C-Max Energi Titanium about 2 months ago, and have been very happy so far. About one month ago, I got a "Stop Safely Now" when starting the car. I pulled the code P0AA6. I reset the DTC, and the car ran fine, but as the car still has the powertrain warranty, I took it to the dealer.  The dealer kept it for a day, told me they couldn't find anything wrong aside from the 12v battery being near-end-of-life, charged me an hour of diagnostic time, and tried to gaslight me saying that code didn't even exist for this car ?. I changed the 12v battery myself, and the worked fine for about a month.

 

Yesterday it happened again, but now it persists. I can still clear it and drive the car, but it returns next on-off cycle.

After some searching, the only interesting info I could find is from a forum discussion of the Ford Escape Hybrid, but seems to hold true here as well:

 

Quote

P0AA6:00
Normal Operation and Fault Conditions
With the ignition in the ON position, the BECM (battery energy control module) monitors the electrical isolation (leakage resistance) between the high-voltage system and the vehicle chassis. The normal resistance value is between 950,000-1,330,000+ ohms. When the engine is run and the resistance value is less than 195,000 ohms, the electrical isolation fault is set. The fault will illuminate the stop safely hazard (red triangle) warning indicator, and the vehicle will not start at the next ignition cycle if the leakage is severe.
Possible Sources
- Moisture/water penetration of high-voltage connectors
- High Voltage Battery cables
- Direct Current/Direct Current (DC/DC) converter control module
- ACCM (air conditioning control module)
- High Voltage Battery
- Electronically Controlled Continuously Variable Transmission (eCVT)
- SOBDMC (hybrid powertrain control module) 

 

So, with this information, I checked the leaks on Forscan. When the car is in "stop safely now" mode, the leakages all read as 1,638,375 ohms. However, (after reset) when the car is running, LEAKRESCON and LEAKRESNEG are still 1,638,375, but LEAKRESPOS and LEAK_RES_OVERALL are around 30,000-40,000 ohms.

So, from this, I'm guessing there is some sort of leak in a harness or module AFTER the contactors (since there is no leak when the contactors are open). I ordered the appropriate wiring manual from ebay, but while I wait for delivery I figured I'd ask the forum to see if anyone has any experience with this issue or any useful suggestions.

[ElectrifyAllTheThings]

So, just to clarify, I don't plan to play with live high-voltage lines. My plan, once I get a good wiring diagram for the high-voltage lines, is to remove the high-voltage service disconnect, then go around the different High Voltage Positive points of the car with a quality multimeter and test the resistance (ohms) to the vehicle chassis. That should lead me to the harness/module that's "shorting out". What I do then will probably depend on whether the offending part is covered by the remaining Powertrain or Hybrid Warranties.

[plus 3 golfer]

Did you get the SM with wiring diagrams as it has the procedures for the DTC?  Yes, the HVB disconnect must be pulled and 12 V battery must be disconnected.  I believe the wiring is only covered under the 3/36 warranty.  There was one poster (maybe on the apparently defunct CMax Energi Forum) had an issue with HVB wiring which was not covered under warranty. The Unique Hybrid Components Warranty (8/100k) should cover the BECM, DCDC, and SOBDMC. 

[ElectrifyAllTheThings]

2 hours ago, Plus 3 Golfer said:

Did you get the SM with wiring diagrams as it has the procedures for the DTC?  

I believe so; I got this one:

 

Quote

Yes, the HVB disconnect must be pulled and 12 V battery must be disconnected.  I believe the wiring is only covered under the 3/36 warranty.  There was one poster (maybe on the apparently defunct CMax Energi Forum) had an issue with HVB wiring which was not covered under warranty. 

That's what I suspected, but it's good to get confirmation.

 

Quote

The Unique Hybrid Components Warranty (8/100k) should cover the BECM, DCDC, and SOBDMC. 

Very useful information! Thanks!

[fbov]

And if you'd like to see the insides before you get there....

https://www.youtube.com/playlist?list=PLIn3FrDiB1lwAhpYXTHmgEJLHwEDPYv2d

 

Scroll down for the several C-Max drivetrain and electrical system videos. He also has one on the HVB disconnect, perhaps not under Ford....

 

Stay well,

Frank

[plus 3 golfer]

The link below is the complete Ford Service Manual and it has the wiring diagrams.  It will have the test procedures for the DTC.

 https://www.ebay.com/itm/Ford-C-Max-2017-2018-Factory-Workshop-Service-Repair-Manual/303621155197?hash=item46b13b297d:g:ST4AAOSw2k5dw5WN

[SnowStorm]

SnowStorm finally ordered his - 2013-2014 of course.  Thanks, +3, for the link.

[ElectrifyAllTheThings]

So, for follow up. The problem seems to have self-resolved after a few days. Looking at this:

Quote

Possible Sources
- Moisture/water penetration of high-voltage connectors

And thinking back, I don't remember about the first time, but it had rained heavily the 2 days before the problem popped up the second time. So, it seems this is the most likely cause. The issue went away and resistance went back up to normal after 2-3 days. It hasn't rained beyond a slight drizzle since then, and the car has continued to operate fine. So, I'll continue to monitor for now.  Maybe look into the seal on the charging port; it seems like the most exposed area where water may come in contact with high-voltage lines.

[Jamison]

Thank you for this. I got stranded near the four corners area with this same problem and I got the car running