John Deere 746.31 – Basic Control Unit (BCU) or Central Control Unit (CCU): Issue With Diff Lock Solenoid

The control unit detects an open circuit or a short circuit in the differential lock solenoid valve circuit while the solenoid valve is active (i.e., when the differential lock is switched on).

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6120 to 6420
• 6120L to 6520L
• 6230
• 6330
• 6430
• 5085M
• 5090M
• 5095M
• 5100M
• 5105M
• 5115M
• 210K
• 315SK
• 444K
• 544K
• 624K
• 724K
• 824K

1. 1

   Electrical Resistance Test: Turn the ignition OFF. Disconnect the differential lock solenoid valve connector (X87 at W13). Measure the resistance between Pin A and Pin B at the solenoid. The specification for standard 12V tractor coils is typically 10 to 12 Ohms at 20°C (68°F).

2. 2

   Wiring Harness Inspection: Check the wiring harness (specifically cables 527 or 310, depending on the model) for open leads, chafing, or short circuits.

3. 3

   Ground Connection Check: Verify that the ground connection to the solenoid is clean, tight, and free of corrosion.

1. 1

   Power Down

   Turn off the engine, remove the key, and ensure the machine is parked safely with the parking brake engaged.

2. 2

   Locate the Solenoid

   Locate the differential lock solenoid valve (Y05) on the transmission/differential housing.

3. 3

   Disconnect and Inspect

   Unplug the electrical connector. Inspect the pins for corrosion, bent terminals, or moisture intrusion. Clean with electrical contact cleaner if necessary.

4. 4

   Test the Coil

   Perform the resistance test outlined above. If the resistance is out of specification (or shows an open circuit/infinite resistance), the solenoid coil is defective and must be replaced.

5. 5

   Replace the Component

   If only the coil is faulty, remove the retaining nut and slide the old coil off the valve cartridge. Slide the new coil on and torque the nut to spec. If the entire valve is faulty or leaking, relieve hydraulic pressure, unscrew the cartridge valve from the housing, and install the new valve assembly.

6. 6

   Reassemble and Clear Codes

   Reconnect the wiring harness, turn the ignition on, clear the BCU/CCU fault codes, and test the differential lock engagement to ensure the code does not return.