Detroit DD15 SPN 97 FMI 3 Water-In-Fuel Sensor Voltage High

Question

I am getting a persistent SPN 97 FMI 3 code on my 2018 Freightliner Cascadia. The dashboard is flashing a water-in-fuel warning even though I just drained the fuel filter bowl and didn't see any moisture. The truck runs fine for now, but I don't want it to derate over a false sensor reading.

Lina Brooks · Accepted Answer

Found the issue. There was a rub-through in the main engine harness about 8 inches back from the WIF sensor connector where it clips to the frame rail. One of the wires was completely severed due to vibration against the loom. I spliced in a new pigtail (Part # A0001534442) using heat-shrink butt connectors and re-routed it with more slack. Code went inactive immediately and hasn't returned after a 500-mile run.

backyard_bart · Answer

Was this after a filter change? Sometimes the sensor gets over-tightened into the plastic bowl and cracks the internal pins. Make sure you only hand-tighten those plastic WIF sensors.

Sarah Thompson · Answer

You might want to check the resistance of the sensor itself. If you unplug it and the code stays FMI 3, the problem is definitely in the harness side. If it switches to a different FMI, your sensor is probably internally shorted.

Marcus Bell · Answer

FMI 3 usually means the circuit is open. Check the wires right where they enter the sensor plug; the Detroit harnesses are known to vibrate and break the copper inside the insulation at that stress point.

Detroit DD15 SPN 97 FMI 3 Water-In-Fuel Sensor Voltage High

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