Case IH 3421 – ENGINE: Fuel Filter Sensor: Voltage Above Max Value

The engine control system is detecting a voltage signal from the fuel filter sensor (water-in-fuel sensor) that exceeds the maximum allowable threshold. This typically indicates an open circuit, a short to power in the sensor wiring, or an internally failed sensor.

• Farmall
• SR175
• SR210
• SR220
• SR250
• SR270
• SV250
• SV280
• SV300
• SV340
• TR270
• TR320
• TR340
• TV370
• TV380
• Maxxum
• Puma
• 1150K
• 1850K
• 721D
• 845B

1. 1

   Visually inspect the fuel filter sensor (mounted on the fuel filter base/bracket) and housing for physical damage or fuel leaks.

2. 2

   Disconnect the sensor pigtail and check the connector pins for corrosion, water intrusion, or pushed-back pins.

3. 3

   Trace the wiring harness back to the Engine ECU. Look for chafed wires rubbing against the engine block or frame.

4. 4

   Test the signal wire for continuity and ensure it is not shorted to a 12V power source (short to power cause).

5. 5

   If the wiring harness tests good, the sensor itself has likely failed internally (open circuit cause).

1. 1

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical shorts.

2. 2

   Locate the fuel filter assembly (usually on the side of the engine block).

3. 3

   Place a small catch pan under the fuel filter to catch any residual diesel fuel.

4. 4

   Unplug the electrical connector from the fuel filter sensor.

5. 5

   If the wiring harness was found to be damaged during diagnostics, repair the broken/shorted wires using appropriate weather-sealed connectors.

6. 6

   If the sensor is faulty, unscrew the old sensor from the fuel filter base.

7. 7

   Install the new sensor (ensure the O-ring or sealing washer is in place) and tighten to OEM specifications.

8. 8

   Reconnect the electrical plug.

9. 9

   Bleed the fuel system if necessary (using the air bleed screw on the fuel filter bracket).

10. 10

    Reconnect the battery.

11. 11

    Use the Case IH Electronic Service Tool (EST) or a compatible CAN-BUS DTC eraser to clear the 3421 fault code from the Engine ECU.

12. 12

    Start the engine and verify the code does not return.