Case IH 3423 – Engine ECU: Fuel Filter Sensor: Implausible Value

The Engine Control Module is receiving an electrical signal from the fuel filter restriction sensor that falls outside the normal, expected voltage parameters. This indicates an electrical anomaly such as an open circuit, a short to ground, a short to power, or a failed internal sensor resistor.

• Farmall
• Steiger 380
• Steiger 385
• Steiger 430
• Steiger 435
• Steiger 485
• STX380
• STX430
• 7120
• 8120
• 8250
• 9250
• Farmall 105U
• Skid Steers

1. 1

   Inspect the pigtail connector and wiring harness at the bottom of the fuel filter for broken wires, chafing, or corrosion inside the plug.

2. 2

   Check the bottom of the primary fuel filter where the sensor threads in for fuel leaks caused by a degraded O-ring.

3. 3

   Drain any accumulated water from the primary fuel filter housing to ensure water intrusion isn't shorting the sensor probes.

4. 4

   Use a multimeter to test the sensor for an internal short or open circuit.

5. 5

   Verify the fuel filter itself is not severely collapsed or restricted.

1. 1

   Turn off the machine, lower all implements, and allow the engine to cool.

2. 2

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

3. 3

   Place a catch pan directly underneath the fuel filter to catch any spilled diesel.

4. 4

   Disconnect the electrical wiring harness from the clogged fuel filter indicator sensor.

   The sensor is threaded into the bottom of the filter housing.

5. 5

   Carefully unscrew the sensor from the bottom of the fuel filter.

6. 6

   If the wiring harness is damaged, splice in a new connector pigtail. If the sensor is faulty, prepare the replacement sensor.

7. 7

   Lubricate the O-ring on the new sensor with clean diesel fuel.

   This prevents pinching or tearing (a common cause of leaks after replacement).

8. 8

   Thread the new sensor into the bottom of the fuel filter and tighten it securely.

   Do not overtighten, as the plastic threads can strip.

9. 9

   Reconnect the electrical harness plug to the sensor.

10. 10

    Prime the fuel system using the manual primer pump.

    This purges any air introduced into the lines during the swap.

11. 11

    Start the engine, verify there are no fuel leaks at the bottom of the filter, and confirm that fault code 3423 has cleared from the dash/monitor.