Case IH 2645 – Transmission Control Unit (TCU / TECU): Hydrostatic unit negative solenoid open circuit

The fault code 2645 indicates an issue with the Hydrostatic unit negative solenoid being in an open circuit condition. This means the electrical path to the solenoid is broken, typically caused by a disconnected plug, a severed or chafed wire in the harness, corroded connector pins, or an internal failure (burnt-out coil) within the solenoid itself.

• Steiger T4B
• Case IH Puma CVX
• Case IH Maxxum CVX

1. 1

   Visually inspect the wiring harness routing down to the CVT hydrostatic unit for chafed insulation, broken wires, or damage caused by debris or heat.

2. 2

   Disconnect the harness at the negative solenoid and inspect the pins for corrosion, moisture intrusion, or pushed-back terminals.

3. 3

   Perform a solenoid coil resistance test using a multimeter across the pins of the negative solenoid. An infinite (OL) or out-of-spec reading indicates the coil is internally open and has failed.

4. 4

   Perform a harness continuity test by disconnecting the harness from the Transmission Controller and measuring resistance from the signal contact to the solenoid connector. Resistance higher than 5.0 ohms indicates an open circuit in the machine harness.

1. 1

   Safely secure the machine

   Park the tractor on a level surface, engage the parking brake, turn the key switch to the OFF position, and turn off the battery disconnect switch.

2. 2

   Access the Hydrostatic Unit

   Locate the hydrostatic unit on the side of the CVT transmission housing.

3. 3

   Address Harness Issues

   If the diagnostic tests revealed a broken wire, repair the wire using OEM-approved splice connectors and heat shrink, or replace the affected harness section.

4. 4

   Replace the Solenoid

   Clean the area around the negative solenoid to prevent dirt from entering the hydraulic system. Disconnect the electrical connector, unbolt/unscrew the failed negative solenoid from the transmission valve manifold, lubricate the O-rings on the new solenoid with clean hydraulic fluid, and install the new solenoid and torque to OEM specifications.

5. 5

   Reassembly and Testing

   Reconnect the harness connector securely. Turn on the battery disconnect switch, start the tractor, and use a diagnostic scan tool to clear the inactive fault code 2645. Test drive the tractor to ensure normal CVT operation and verify the code does not return.