Case IH 3688 (DTC 4F15) - ECU – Engine ECU: Water in fuel sensor or sensor circuit failure

The engine control system has detected an electrical fault (such as an open load, short circuit, or voltage out of range) in the water-in-fuel (WIF) sensor or its wiring harness.

• MAXXUM T4E
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Puma Series (130 through 240)
• Maxxum Series (115 through 150)
• Steiger Series
• Magnum Series
• Farmall/JXU series

1. 1

   Drain the primary fuel filter/water separator to empty any accumulated water or debris

2. 2

   Inspect the wiring harness leading to the bottom of the fuel filter for frayed wires, rubbed-through insulation, or corrosion inside the connector plug

3. 3

   Verify that no engine sensor fuses are blown in the fuse panel

4. 4

   Isolate the sensor: if the wiring is intact, the filter is drained, and the monitor continues to beep or flash the error, the sensor has failed internally

1. 1

   Turn off machine

   Turn off the machine, remove the key, and allow the engine to cool.

2. 2

   Locate filter assembly

   Locate the primary fuel filter / water separator assembly on the engine block or chassis frame.

3. 3

   Disconnect electrical connector

   Disconnect the electrical connector from the water-in-fuel sensor, which is threaded into the bottom of the fuel filter.

4. 4

   Drain fuel

   Place a catch pan underneath and open the drain valve to empty the fuel from the filter housing, preventing a spill.

5. 5

   Remove faulty sensor

   Unscrew the faulty water-in-fuel sensor from the bottom of the filter. (Note: Many technicians opt to replace the entire fuel filter at this time to ensure no algae or debris damages the new sensor).

6. 6

   Install new sensor

   Lubricate the O-ring on the new water-in-fuel sensor with a small amount of clean diesel fuel and thread it into the bottom of the filter housing. Do not overtighten.

7. 7

   Reconnect electrical connector

   Reconnect the electrical connector to the new sensor.

8. 8

   Prime fuel system

   Prime the fuel system using the manual primer pump to remove any air pockets introduced during the repair.

9. 9

   Verify repair

   Start the engine and verify that the fault code clears from the cab monitor.