Case IH 2644 – TCM / TCU: Hydrostatic unit positive solenoid is open circuit

The fault indicates an "open circuit" in the electrical path of the "Hydrostatic unit positive solenoid". An open circuit means the control module is attempting to send a voltage signal to the solenoid but detects zero current flow. This is almost always caused by a broken wire, a disconnected or corroded electrical plug, or a burnt-out (failed) solenoid coil.

• Steiger T4B
• Puma CVX
• Maxxum CVX
• Optum CVX

1. 1

   Visual Inspection: Inspect the wiring harness running from the TCM/TCU to the hydrostatic unit on the transmission. Look for visible breaks, chafing, or disconnected plugs.

2. 2

   Coil Resistance Test: Disconnect the electrical connector at the positive solenoid. Use a digital multimeter to measure the resistance (Ohms) across the solenoid coil's pins. An infinite reading (OL) confirms the solenoid coil is internally broken (open) and must be replaced.

3. 3

   Harness Continuity Test: If the coil tests within normal resistance specs (usually a few Ohms), check the connector pins for corrosion or pushed-back terminals. Measure for continuity between the solenoid connector and the corresponding pins on the TCM/TCU harness to rule out a broken wire in the loom.

1. 1

   Prepare machine

   Park the tractor on a level surface, engage the parking brake, and turn off the engine. Disconnect the battery ground cable to prevent short circuits.

2. 2

   Locate solenoid

   Locate the hydrostatic unit on the side of the CVT transmission housing. Identify the "positive" solenoid (refer to the specific model's service manual diagram to distinguish it from the "negative" solenoid).

3. 3

   Disconnect harness

   Disconnect the electrical wiring harness from the solenoid.

4. 4

   Clean area

   Thoroughly clean the area around the solenoid to prevent dirt and debris from entering the hydraulic system.

5. 5

   Remove solenoid coil

   Remove the retaining nut or bolts holding the solenoid coil to the valve stem. (Note: If the valve and coil are a single integrated cartridge, unthread the entire cartridge from the manifold).

6. 6

   Install new coil

   Slide the old coil off. Install the new solenoid coil (or cartridge), ensuring any O-rings are lubricated with clean hydraulic oil. Torque the retaining nut to OEM specifications.

7. 7

   Reconnect components

   Reconnect the electrical harness and the battery ground cable.

8. 8

   Clear codes and test

   Clear the fault codes using the tractor's diagnostic display or a dealer service tool. Perform a test drive to verify the transmission shifts smoothly and the code does not return.