Case IH 2123 (6155.06) - DEC – Transmission Control Unit (TCU) or Vehicle Control Module (VCM / Armrest Controller): Synchro 4 Solenoid - LSD short to HSD

Low Side Driver short to High Side Driver. The voltage supply is bypassing the electrical load and going straight to the control ground, or the internal windings of the solenoid coil have melted together and shorted out. This prevents the Synchro 4 solenoid from engaging its respective transmission gear or range.

• MAXXUM T4E
• CX (Synchro)
• MC
• MTX
• MX
• XTX
• Puma
• Maxxum series
• 580M
• 580N
• 590 Super N
• 585G
• 586G
• 588G

1. 1

   Inspect the transmission wiring harness leading to the Synchro 4 solenoid for pinched wires, melted insulation, or chafing against the transmission housing.

2. 2

   Disconnect the electrical connector at the Synchro 4 solenoid and measure resistance across the two pins (should be around 7.3 Ohms; 0 Ohms indicates an internal short).

3. 3

   With the solenoid and TCU harness disconnected, test for continuity between the High Side and Low Side wires in the harness to check for a harness short.

4. 4

   Inspect the solenoid and harness connectors for water ingress, mud, or corrosion that could bridge the pins.

1. 1

   Safely park the machine on level ground, engage the parking brake, turn off the engine, and disconnect the battery to prevent TCU damage.

2. 2

   Locate the transmission valve block and identify the Synchro 4 solenoid.

3. 3

   Thoroughly clean the area around the solenoid with brake cleaner and compressed air to prevent dirt from entering the transmission hydraulic circuit.

4. 4

   Disconnect the electrical connector from the solenoid.

5. 5

   Remove the retaining nut, bolt, or snap-ring holding the solenoid coil to the valve cartridge (depending on the specific valve block design).

6. 6

   Slide the old solenoid coil off the valve stem.

   Note: If replacing the entire synchronizer valve assembly, unthread the cartridge from the block and catch any escaping hydraulic fluid.

7. 7

   Lubricate the O-rings on the new solenoid/valve with clean transmission fluid.

8. 8

   Slide the new coil onto the stem and secure it with the retaining hardware, torquing to OEM specifications.

9. 9

   Reconnect the electrical connector, ensuring the weather seal is intact.

10. 10

    Reconnect the battery, clear the fault codes using a diagnostic tool, and test drive the machine to verify the transmission shifts correctly into the Synchro 4 gear ranges.