New Holland 3390 – TCU: Fan Rotational Speed Not Detected on Viscous Coupling

The Transmission Control Unit (TCU) has lost the signal from the speed sensor integrated into the electronically controlled viscous fan drive. The system is unable to detect the rotational speed of the cooling fan, which can result in improper engine cooling and system performance issues. The fan may default to a high-speed state causing excessive noise and fuel consumption, or it may fail to engage, leading to overheating under load.

• New Holland T8 Series
• T8.275
• T8.390
• T8.435
• Magnum 340
• Magnum 235-340
• New Holland T8000 Series
• TG Series
• MX Series
• T8010-T8050
• TG215-TG305

1. 1

   Visually inspect the fan drive assembly for any signs of silicone fluid leakage and check the fan blades for cracks or damage

2. 2

   Inspect the wiring harness and connector leading to the viscous fan drive for damage, abrasion, or corrosion, paying close attention to the connection at the fan clutch

3. 3

   Examine the wiring harness for proximity to hot engine or exhaust components that could cause a temperature-related open circuit or short

4. 4

   With the key on but engine off, check for correct voltage supply and ground at the fan clutch connector

5. 5

   Perform a pin drag test on the connector terminals to ensure they make a tight connection and rule out loose pins

6. 6

   Inquire with a dealer about available software updates for the tractor's control modules, as this has resolved fan control issues in some instances

1. 1

   Verify fault codes

   Use a diagnostic tool to confirm that fault code 3390 is active or has been logged. Note any other related fault codes.

2. 2

   Perform solenoid test

   Disconnect the fan clutch connector. Apply a 12V source to the solenoid power and ground pins. You should measure a current draw between 1.0 and 2.0 Amps.

3. 3

   Test speed sensor signal

   With the engine cold, connect a multimeter capable of measuring frequency to the speed sensor signal and ground wires. Run the engine at 1500 RPM. The expected frequency is 10-130 Hz for a disengaged fan. An absence of a frequency signal while the fan is rotating points to a failed internal sensor.

4. 4

   Replace viscous fan drive assembly

   If the sensor signal is absent or erratic and all wiring is intact, replace the viscous fan drive assembly. Carefully remove the fan and clutch, being cautious not to damage the radiator fins, separate and inspect the blade, and install the new clutch. Keep the new clutch in a vertical position during handling and installation to ensure internal silicone fluid is properly distributed. Tighten all fasteners to the manufacturer's specified torque.

5. 5

   Clear codes and verify

   After installation, clear all fault codes with a diagnostic tool and run the tractor to verify that the repair is successful and the code does not return.