I’m going crazy on this one.
The story is as follows:
2008 Ford C-Max Titanium 2.0 Diesel Automatic.
Starts with messages about P238, P236, U2023, U1900, P1335 and can bus messages.
I clear the messages with OBD and they keep coming back. Transmission error messages, limp mode, the whole 9 yards.
All the while the ABS light is on the dash. After moving the passenger seat, I suspected that there was a connection problem there.
I pulled off the battery cable and pretty much pulled down all the cable and connectors looking for problem spots. I pulled the BCM fuse panel and checked every fuse. I even opened the two connectors on the side panel looking for rust, poor connections.
Nothing visible, no corrosion, no loose wires. Reassembled everything and checked the ground wires behind the left front headlight, a problem I saw on Youtube. Replaced them for good measure.
Finally decided there was nothing more to do so I decide to put it away for the day. Got in and turned the key and nothing happened.
Nothing. The dash message centre was lit but no diagnostic lamps, no oil lamp, no abs lamp, no engine light, no matter where I turned the key there was no response. The radio works and the keyless lock works but the windows won’t go up. The blinkers don’t work and the headlights are out. I can’t get it out of park and there is no response from the OBD port. I was stunned. This had never happened.
Panic mode. I pulled the ECU looking for poor contacts, and the GEM, again looking for bad contacts. Checked every single fuse twice, both under the dash and in the engine bay. I went over everything I did that day and couldn’t find any mistakes that would cause that.
BTW, I had pulled the dash out and did the soldering trick a week before trying to get to the bottom of the spurious messages. Car ran fine after that so I pretty much rule that out.

I’ve even gone so far as to pull the ECU and force the lid off to clean and solder the contacts. There was signs of humidity around some areas so I cleaned it with a toothbrush and electronic cleaner. Carefully soldered the 60 or so contacts but to no avail.
I have a fine soldering pen and am skilled at soldering, so no overlap or shorts.

I am desperate! What would cause this? No power to the ECU? Defect GEM? Seems like there is no power to the instrument electronics. Where does it get it’s power, from the GEM?
Anybody got any tips; I don’t want to sell this car for parts.
Cheers…

I'm so sorry. I wrote 

"All the while the ABS light is on the dash..."

I meant "All the while the AIRBAG light is on the dash..."

It should have been logical even though I didn’t see it. It turned out that the large connector on the passenger sidewall was not totally in place, despite opening it and checking several times. It wasn’t until I took it off the sidewall that I realized the pins weren’t seating properly.

 

Turns out that it is a geared handle lock on the connector and I was engaging only the second latch instead of the whole gear. Dumb, right? Well, I have to admit when I do something stupid so other people don’t make the same mistake.

Now we know…