Case IH 3423 – Engine Control Unit (ECU): Fuel Filter Sensor: Implausible Value

This code is triggered when the engine control system receives a signal from the fuel filter sensor (typically the water-in-fuel sensor located on the primary fuel filter/water separator) that does not make logical sense based on the engine's current operating parameters.

• skid steer
• Farmall 100C
• Farmall 115U
• Farmall 65C
• SR175
• L220
• L230
• C238
• T4.75
• T4.100
• T5.120

1. 1

   Inspect the wiring harness leading to the fuel filter sensor for chafing, breaks, or melted insulation. Disconnect the sensor and inspect the pins for corrosion, moisture, or a loose fit.

2. 2

   Drain the water separator by opening the drain valve at the bottom of the filter to remove any accumulated water and sediment, which can cause an implausible reading.

3. 3

   Check for related codes such as 3421 (Voltage Above Max), 3422 (Voltage Below Minimum), or 3424 (Fuel Filter Clogged) to help isolate whether the issue is a dead short, an open circuit, or a physical blockage.

4. 4

   Use a multimeter to verify that the sensor is receiving the correct reference voltage from the ECU and that the ground circuit is intact.

1. 1

   Preparation

   Turn off the machine, remove the key, and allow the engine to cool. Place a drain pan beneath the primary fuel filter assembly.

2. 2

   Disconnect

   Unplug the electrical connector from the fuel filter sensor located at the bottom of the fuel filter.

3. 3

   Drain the Filter

   Open the petcock/drain valve on the sensor to drain the fuel from the filter housing into the pan.

4. 4

   Remove the Sensor/Filter

   If only replacing the sensor: Carefully unscrew the sensor from the bottom of the filter housing. If replacing the filter (recommended if contamination is present): Use a filter wrench to remove the spin-on fuel filter, then unscrew the sensor from the old filter.

5. 5

   Installation

   Lubricate the O-ring on the new sensor with a small amount of clean diesel fuel. Thread the new sensor into the fuel filter (hand-tighten to avoid cracking the plastic housing). If installing a new filter, lubricate its gasket and spin it onto the filter head.

6. 6

   Reconnect

   Plug the electrical connector back into the new sensor.

7. 7

   Prime the System

   Turn the ignition key to the ON position (without starting the engine) to allow the electric lift pump to prime the fuel system and purge air. You may need to cycle the key a few times.

8. 8

   Test

   Start the engine and inspect the filter and sensor area for any fuel leaks.

9. 9

   Clear Codes

   Use an Electronic Service Tool (EST) or diagnostic scanner to clear the 3423 fault code from the Engine ECU.