2016 Energi Yellow Wrench/Stop Safely Now and power loss while driving on freeway

[maxmapper]

I bought a used 2016 C-Max Energi with ~30K miles. Driving it home from the dealership on the freeway with a 1/4 tank of gas it abruptly showed the yellow wrench icon and a 'See Manual' message and went into limp mode (5MPH max). Obviously quite scary and dangerous to be reduced to 5MPH max speed on the freeway. I tested the voltage of the 12V battery and it was at 12.2 volts so I thought it might be related to the original battery not holding a charge anymore. A new 12v battery didn't seem to fix the problem as the yellow wrench/power loss has happened again two more days in a row. If I let the car sit for an hour or two it will finally start up again and let me drive it home. I am now going to take it to the dealership, but any recommendations on how I can troubleshoot this issue or get the dealership to reproduce the issue would be very helpful, as it seems to only happen after driving for a few hours. In Engineering Test Mode there are no fault codes stored, but I have not yet done an ODB scan.

When the car fails during driving, I get the following messages:

https://imgur.com/a/m8rsuek

• Check Park Aid

• See Manual

• Stop Safely Now

• Check Engine Light

• Yellow Wrench Light

• Red Triangle Exclamation Point Light

Then for the hour or two the car refuses to start, I press the brake and press the ignition button and I hear a click in the battery compartment but the car does not reach Ready To Drive, it fails to startup and instead shows me the following errors on the left instrument panel screen:

https://imgur.com/a/W3C5hA0

• See Manual

• Park Aid Fault

• Check Park Aid

• On the infotainment screen at this time it displays this (not sure why?) "Vehicle charge. Your vehicle is set to be fully charged at" https://i.imgur.com/ZJfjlrJ.png. There is no charge icon on the dash, so I'm not sure if this is just an infotainment bug related to the yellow wrench or something serious?

The last time this happened the 12v battery was at 12.45 volts. When I started the drive the 12V battery was above 12.6V. From what I understand 12.45 is borderline low but shouldn't prevent the car from starting? I have confirmed when my car is running normally it is supplying 14V to the 12V battery as expected.

[maxmapper]

I scanned DTC codes using 2 adapters, an ELM327 one using ODB Doctor and a Vgate vlinker FD using Forscan Demo. These are taken when the car is working, aka after turning on the car while Ready To Drive is showing (the car is not currently showing the yellow wrench):

 

ELM327:

P2800

U1028

P1A13

P26C3

P2801

P2802

U0198

U1028

P1A13

 

FORScan 

P2800

U0198

U1028

P26C3

P2801

P2802

U3003

U0401

U0452

U0402

 

Looking these up a bit I found this TSB SSM 47790 https://static.nhtsa.gov/odi/tsbs/2019/MC-10155562-9999.pdf. Does anyone have the wiring diagram for a 2016 C-Max Energi so I can "On C-Max, inspect connectors C134, C140, C144, C1651, C1717 and C1812 and service as necessary."?

Edited January 26, 2023 by maxmapper
updating DTCs

[oldbeyondmeasure]

The attached document is for a 2017 C-Max Energi, so I don't know if it applies to yours, but take a look at the diagrams beginning on page 2-20. 

2017-C-Max-Modifiers-Guide.pdf

[maxmapper]

Just wanted to update this thread. The dealership was able to reproduce the Stop Safely Now message while they had it in the shop. They did some pinpoint tests and determined it was the transmission range sensor wiring harness which was faulty. Apparently this is internal to the HF35 transmission. They can't service the HF35 internally so they had to replace the whole transmission. The HF35's are backordered at the moment so it took 6 weeks but was covered under warranty.