Somewhere in the quiet stretch between Montreal and Ottawa, we got a call that started like many others — “Truck won’t move, engine shuts off randomly.” What followed turned out to be one of our most bizarre on-the-road rescues yet.
Our tech arrived to find a late-model Freightliner that would start fine, run for a few minutes, then mysteriously stall — no fault codes, no warning lights, nothing. The driver had already changed the fuel filters and swapped batteries. Still dead on arrival.
We dug deep. With the laptop hooked up, we monitored live data and spotted tiny voltage drops on the CAN line just before each shutdown. A classic case of ghost signals.
The culprit? A shorted DEF level sensor buried in the tank wiring harness — it was backfeeding just enough noise to crash the entire ECM. Even worse, it only happened once the tank warmed up and pressure changed. Total needle-in-a-haystack problem.
We bypassed the sensor temporarily, isolated the faulty wire, and manually initiated a regen to clear all related derates. The truck roared back to life and didn’t stall again — the driver made it to Ottawa with time to spare and a whole new appreciation for our team.
Sometimes, it’s not the big stuff that breaks you — it’s the invisible stuff you can’t see, unless you really know where to look.
