Case IH 2122 (6155.03) - DEC – Transmission Control Unit (TCU): Synchro 4 Solenoid - LSD short to high voltage

Indicates an electrical fault in the transmission control system where the controller detects 12 volts on the ground-control circuit when it shouldn't be. This typically means the wire has chafed and is touching a live power wire, or the solenoid itself has failed internally and is bleeding voltage into the ground circuit.

• MAXXUM T4E
• CX50
• CX60
• CX70
• CX80
• CX90
• CX100
• MX80C
• MX90C
• MX100C
• MC Series
• MTX Series
• Puma
• Steiger

1. 1

   Visually inspect the wiring harness running from the transmission valve block to the transmission controller for pinched wires, melted insulation, or areas where the harness rubs against the chassis.

2. 2

   Disconnect the Synchro 4 solenoid and inspect the connector pins for corrosion, water ingress, or bent terminals.

3. 3

   Perform a voltage test: With the key ON and the solenoid disconnected, use a multimeter to check the Low Side (ground) pin on the harness side. If it reads 12V, the wiring harness has a short to power.

4. 4

   Perform a resistance test: Measure the resistance across the pins of the Synchro 4 solenoid itself. If the resistance is out of specification or shows continuity to the solenoid casing, the solenoid coil is internally shorted.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the negative battery terminal to prevent further electrical damage.

2. 2

   Isolate the Short

   Based on your diagnostic tests, if the harness is shorted, trace the wire back to the TCU and repair the chafed section using proper automotive-grade wire and heat-shrink tubing.

3. 3

   Replace the Solenoid (If Faulty)

   If the solenoid coil failed the resistance test, remove the retaining nut/clip on the transmission valve block and slide the old coil off the valve stem.

4. 4

   Install New Part

   Slide the new solenoid coil onto the valve assembly and secure it. Reconnect the wiring harness.

5. 5

   Recalibrate

   Reconnect the battery. Clear the stored fault codes using a diagnostic tool or the Universal Display Plus monitor. Perform a transmission/clutch calibration procedure, as replacing synchronizer components often requires the TCU to relearn the engagement points.