Case IH 2120 (6156.06) - DEC – DEC: Synchro 5 Solenoid - LSD short to HSD

The fault indicates a Low Side Driver (LSD) short to High Side Driver (HSD) on the Synchro 5 Solenoid circuit. The ground wire is shorted directly to 12V power, preventing the control module from grounding the circuit, leaving the Synchro 5 solenoid unable to actuate or causing it to lock up.

• MAXXUM T4E
• Maxxum
• Puma
• Magnum
• Steiger
• T6
• T7
• T8

1. 1

   Visually inspect the transmission wiring harness routing from the DEC to the transmission valve block for chafed insulation, pinched wires, or rubbing against the housing.

2. 2

   Disconnect the Synchro 5 solenoid connector and the DEC harness connector to inspect pins for corrosion, water ingress, or bent terminals.

3. 3

   With the key ON (engine OFF) and solenoid disconnected, probe the ground wire (LSD) at the solenoid connector. A 12V reading indicates a short in the wiring harness.

4. 4

   Measure the resistance across the two pins of the Synchro 5 solenoid. Near zero ohms indicates the solenoid is internally shorted and must be replaced.

1. 1

   Preparation

   Park the tractor on a level surface, engage the parking brake, lower all implements, turn off the engine, and disconnect the negative battery cable.

2. 2

   Locate the Solenoid

   Locate the transmission control valve block (typically mounted on the side of the transmission housing or rear axle center housing). Identify the Synchro 5 solenoid.

3. 3

   Harness Repair

   If the diagnostic tests revealed a harness short, cut out the melted/chafed section of the wire and solder/heat-shrink a new section of wire, or replace the affected transmission harness sub-assembly.

4. 4

   Solenoid Replacement

   Clean the area around the valve block thoroughly. Disconnect the electrical connector from the Synchro 5 solenoid, remove the retaining bolt or snap-ring, and pull the faulty solenoid straight out. Lubricate the O-rings on the new solenoid with clean transmission fluid, insert it into the bore, and secure it.

5. 5

   Reassembly & Calibration

   Reconnect the electrical connector and the battery. Turn the key ON and clear the inactive fault codes via the instrument cluster 'H-Menu' or the electronic service tool.

6. 6

   Synchronizer Calibration

   Perform a transmission synchronizer and clutch calibration (often requiring the transmission oil to be heated to at least 45°C/113°F) so the DEC can learn the engagement points of the new solenoid.