2018 Freightliner Cascadia DD15 - SPN 97 FMI 3 Water in Fuel sensor error

Question

I am getting a constant dash warning for Water in Fuel along with SPN 97 FMI 3. I have already drained the primary fuel filter bowl and there is no visible water in the fuel sample. The code is active and will not clear even after draining the separator.

Kevin Tran · Accepted Answer

The issue was a broken signal wire about 6 inches back from the WIF sensor connector in the main engine harness loom. I performed a voltage drop test and found the wire had failed internally due to vibration. I cut out the bad section, soldered in a new 18-gauge wire with heat-shrink butt connectors, and the SPN 97 code went inactive immediately. Total cost was just the price of the repair kit and about two hours of tracing.

road_rambler · Answer

FMI 3 almost always indicates an open circuit or a short to power. Check the harness pigtail near the bottom of the Davco filter housing, as those wires tend to rub against the frame rail and break inside the insulation.

Carlos Diaz · Answer

You should check your grounding. Use a multimeter to see if you have 5V reference at the sensor plug. If you see battery voltage there instead of the reference signal, you have a harness short.

Lina Brooks · Answer

Sometimes the pins inside the sensor itself get corroded from salt spray. Spray some electrical contact cleaner in the connector and look for any green crusties on the sensor pins.

2018 Freightliner Cascadia DD15 - SPN 97 FMI 3 Water in Fuel sensor error

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