Case IH 566-05 - DEC – DEC: Rear differential lock control solenoid electrical circuit fault - current below normal

The control module is commanding the rear differential lock solenoid to engage, but it is not detecting the expected electrical current flowing through the circuit. This condition is almost always caused by a disconnected plug, a broken/cut wire in the harness, or an internally failed (open) solenoid coil.

• MAGNUM AFS Connect
• Maxxum Series Tractors (5120, 5130, 5140, 5150, 5220, 5230, 5240, 5250)
• 3000 & 4000 Series Tractors (3220, 3230, 4210, 4230, 4240)
• Magnum Series Tractors
• Combines (2144, 2166, 2188, 2344)
• 580L Series 2 Loader Backhoes

1. 1

   Visually inspect the rear differential lock solenoid and its 2-terminal connector to ensure it is securely plugged in and free of dirt, water, or corrosion.

2. 2

   Inspect the wiring harness leading from the DEC to the solenoid for chafing, pinch points, or severed wires.

3. 3

   Perform a solenoid coil resistance test: disconnect the 2-terminal connector and use a multimeter set to Ohms (Ω) across the solenoid pins. An 'OL' (Open Loop) reading indicates a broken internal coil.

4. 4

   Check the voltage supply: with the connector unplugged, turn the key ON and engage the differential lock switch in the cab. Measure voltage at the harness side to verify the DEC is sending a 12V signal.

1. 1

   Park the machine

   Park the machine on a level surface, turn the engine off, and engage the parking brake.

2. 2

   Clean the area

   Clean the area around the differential lock hydraulic valve block to prevent dirt from entering the hydraulic system.

3. 3

   Disconnect the connector

   Disconnect the 2-terminal electrical connector from the failed solenoid.

4. 4

   Remove retaining hardware

   Remove the retaining nut or snap-ring at the end of the valve stem that holds the solenoid coil in place.

5. 5

   Remove old solenoid

   Slide the old solenoid coil off the hydraulic valve cartridge. (Note: You usually do not need to remove the hydraulic valve cartridge itself, which prevents fluid loss).

6. 6

   Install new solenoid

   Slide the new replacement solenoid onto the valve stem and secure it with the retaining nut/snap-ring.

7. 7

   Reconnect the plug

   Reconnect the 2-terminal electrical plug.

8. 8

   Clear fault code

   Turn the key ON and use the tractor's diagnostic menu or a service tool to clear the inactive 566-05 fault code.

9. 9

   Test the system

   Test the differential lock switch to ensure the code does not return and the lock engages properly.