Massey Ferguson 977.05 – Engine Control Unit (ECU): Engine Cooling Fan Speed Solenoid Issue / Fan control output open circuit

The controller is attempting to command the engine cooling fan speed solenoid (located on the viscous fan clutch) but detects no electrical current flowing through the circuit. This indicates a broken wire, an unplugged connector, or a failed (open) solenoid coil inside the fan clutch.

• 4710
• 7724S
• 5712SL
• Interim Tier 4 (2012-2015)
• 7722
• 7722S
• 7615
• 5613
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7616
• 7618
• 5608
• 4708
• 7619
• 7626
• 7726S
• 7624
• 4707
• 4709
• 5711SL
• 7614
• 7718S
• 5610
• 7620
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 5612
• 7622
• 7720
• Tier 4 (2015-2021)
• 5611
• 7715S
• 5609
• 7724

1. 1

   Visually inspect the wiring harness leading to the viscous fan clutch at the front of the engine for severed wires, heat damage, or chafing against moving parts.

2. 2

   Inspect the electrical connector at the fan clutch to ensure it is fully seated. Disconnect it and check for corroded, pushed-back, or moisture-damaged pins.

3. 3

   Using a multimeter, measure the resistance across the pins on the fan clutch solenoid itself. An infinite resistance (OL) reading indicates the internal solenoid coil has failed open.

4. 4

   If the solenoid tests good, check for continuity on the wiring harness between the fan clutch connector and the ECU to locate a break in the wiring.

1. 1

   Disconnect Battery

   Always disconnect the negative battery terminal before performing electrical repairs.

2. 2

   Repair Wiring

   If the diagnostic checks reveal a broken wire in the fan control harness, repair the wire using heat-shrink butt connectors, or replace the fan control wiring sub-harness entirely if it is heavily degraded by engine heat.

3. 3

   Replace Fan Clutch

   If the solenoid coil inside the fan clutch is open, the clutch assembly must be replaced. Remove the fan shroud and drive belts as necessary, unbolt the fan blade assembly from the viscous clutch, remove the viscous clutch from the engine mounting hub, install the new viscous fan clutch, reattach the fan blades, and torque to OEM specifications.

4. 4

   Reconnect and Clear Codes

   Reconnect the electrical harness, reconnect the battery, and start the tractor. Verify the fan operates correctly and use a diagnostic tool to clear the 000977.05 code.