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

This code indicates that the engine control module is receiving a voltage signal from the fuel filter sensor (commonly the Water-in-Fuel or WIF sensor) that exceeds the maximum expected threshold. A "Voltage Above Max Value" condition typically points to an open circuit, a disconnected sensor, or a short to a power source (like 5V or 12V) in the sensor's wiring harness.

• skid steer
• Farmall 65C
• Farmall 75C
• Farmall 85C
• Farmall 95C
• Farmall 100C
• Farmall 105U
• Farmall 110C
• Farmall 115C
• Farmall 120C
• SR175
• TR270
• 1150K
• 1850K
• 721D
• 821E
• 845B
• 865B

1. 1

   Inspect the wiring harness and the electrical connector at the fuel filter sensor for physical damage, corrosion, or pushed-out pins

2. 2

   Use a multimeter to check the sensor circuit for an open circuit or a short to voltage. Verify that the sensor is receiving the correct reference voltage and has a solid ground connection

3. 3

   Place a container under the filter and open the sensor/drain valve to drain any accumulated water or debris, which could potentially cause erratic sensor readings

4. 4

   If the connector was simply loose, reconnect it, clear the fault codes using a diagnostic tool, and cycle the key to see if the code returns

1. 1

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

   Ensure the machine is safely shut down before beginning work.

2. 2

   Locate the fuel filter / water separator assembly on the engine.

   Identify the assembly to access the sensor.

3. 3

   Disconnect the electrical harness connector from the fuel filter sensor located at the bottom of the filter assembly.

   Carefully unplug the connector.

4. 4

   Place a suitable drain pan underneath the fuel filter.

   Prepare to catch any draining fuel or water.

5. 5

   Unscrew the fuel filter sensor (which often doubles as the water drainage valve) from the bottom of the filter to drain the fuel and remove the faulty unit.

   Remove the old sensor completely.

6. 6

   Lubricate the O-ring on the new sensor with clean diesel fuel and thread it into the bottom of the fuel filter. Tighten securely (do not over-tighten to avoid cracking the plastic housing).

   Install the new sensor carefully to ensure a proper seal without damaging the housing.

7. 7

   Reconnect the electrical harness to the new sensor.

   Ensure the connection is secure.

8. 8

   Prime the fuel system to remove any air introduced during the repair.

   This is necessary to ensure the engine starts and runs smoothly.

9. 9

   Start the engine and inspect the bottom of the filter for any fuel leaks.

   Verify the repair is leak-free.

10. 10

    Clear the fault code using a diagnostic tool or verify that the code goes inactive after a key cycle.

    Confirm the issue has been resolved.