Ghost in the Mirror

"I don't want to scare you, but ever since this Yukon was at the old, haunted Moundsville Penitentiary, its been having these strange electrical issues."
The 2017 Yukon's strange electrical issues Jim mentioned included intermittent no-starts and stalling, a SVC 4WD message at times on the DIC, and once it set a DTC U0403.
"Anything else?" I asked. It is very important to collect as much information as possible, including where the vehicle called home during its service life.
"Uh, yeah--if you star in the rearview mirror long enough, you'll see the mangled face of a convict that was butchered with a shiv," Jim added.
"That'll ruin your day," I said.
The vehicle started several times for me without a problem. We took it on a road test and the Yukon performed flawlessly. "Would you mind not staring at me in the rearview mirror, Tom?"
"He does look like that convict from Moundsville prison," Jim laughed.
Jim directed me to Moundsville prison: a stoic, imposing stone structure adorned with turrets and battlements, like a castle, its empty cells filled with regret. I pulled into the parking area, turned the ignition off--and then the ghost showed up!
The engine wouldn't shut off. "I can get it to shut down," Jim said. He opened the door and the engine shut off. Then it would not restart--it wouldn't even crank.
"Great place to be stranded," Tom said, "At a haunted prison."
I popped the hood release and grabbed my digital meter. I started at the battery, checking connections.
"They're clean and properly torqued," Jim said. "The starter was replaced about a month ago at another shop in an attempt to fix this thing."
I checked each fuse with my meter. "I checked them," Jim said.
"That's nice, but I'm checking them again," I replied.
Tom had a scan tool plugged in. "There aren't any codes," he said.
I came around to where he sat, behind the steering wheel.
"There's no MIL on," I said, "You should see the MIL with the key on."
I went back to the UBEC and tapped on the ignition main relay that sends ignition power to the ECM.
"The MIL light just turned on," Tom said. I told him to try starting the Yukon. It started.
"Let's get back to the shop," Jim suggested.
We found a poorly-tensioned terminal at connector 2.

That wasn't the end of our diagnostics. When Jim turned the ignition off, the engine kept running until I opened the door. This Yukon came from Mansfield, Ohio. They use a lot of road salt and saline. This acted just like a ground issue. I looked at the schematic and spotted a splice location under a sill plate. Sure enough, the white, salty film was under the plate. J308 had been eaten alive by sodium chloride.

No more ghosts!!