Case IH 3390 – Engine Controller (ECM / EDC): Viscous fan speed not detected.

Triggered when the engine controller loses the speed signal from the viscous fan speed sensor. The system relies on this sensor to monitor the fan's RPMs as it adjusts cooling based on engine and transmission temperatures. When the controller commands the fan to increase speed but does not detect a corresponding RPM signal, it logs this fault.

• Steiger T4B
• Magnum 215
• Magnum 245
• Magnum 275
• Magnum 305
• Magnum 335
• Magnum 340
• MX215
• MX245
• MX275
• MX305
• Steiger 350
• Machines utilizing F5C engines

1. 1

   Check for intermittent wiring breaks by physically manipulating ('pulling on') the wiring harness near the fan clutch while the machine is running at operating temperature (approx. 200°F).

2. 2

   Test the wiring harness from the viscous fan connector back to the ECM/TCU for continuity, shorts to ground, or shorts to power.

3. 3

   Check for related fan driver circuit codes (e.g., 3384 or 3385) that might indicate a short rather than just a missing speed signal.

1. 1

   Inspect the Harness

   Carefully inspect the OEM harness pins (specifically checking for pushed-out pins or corrosion at the fan clutch connector).

2. 2

   Repair Wiring

   If a break or short is found in the harness during the physical 'pull test' or multimeter continuity test, repair the wiring harness or replace the pigtail connector.

3. 3

   Replace the Viscous Fan Clutch

   If the wiring tests perfectly fine under load and temperature, the internal speed sensor on the viscous fan drive has failed. The sensor is integrated into the clutch assembly, meaning the entire viscous fan drive must be replaced.

4. 4

   Clear Codes

   After replacing the fan clutch or repairing the harness, use an Electronic Service Tool (EST) or a Can-Bus DTC Eraser to clear the inactive fault codes from the ECM.

5. 5

   Test Drive

   Run the tractor under load (e.g., pulling an implement) until the engine and transmission reach operating temperature (approx. 200°F) to verify the fan revs up properly without losing the speed signal.