Case IH 734-16 - DEC – Transmission Control Unit (TCU): Transmission C1 clutch solenoid electrical circuit fault voltage high

The Transmission Control Unit (TCU) has detected that the voltage on the electrical circuit controlling the C1 clutch solenoid is above the normal operating range. This is typically caused by a short to a high power source (B+), an overcharging alternator, or an internal failure within the solenoid coil itself.

• MAGNUM AFS Connect
• Case IH MX Series Magnum Tractors (MX210, MX230, MX245, MX255, MX285)
• Case IH Magnum Series (235, 260, 290, 315, 340, 370)

1. 1

   Test battery voltage at the terminals (should be 12 to 14 volts). If excessively high, test the alternator output to determine if it is overcharging the system.

2. 2

   Check for an external power supply shorted to the controller power supply (specifically check cavity 12 of connector C058, if applicable).

3. 3

   Remove the controller cover from the rear of the tractor and visually inspect the wiring harness routing from the transmission controller down toward the transmission solenoids under the cab for rubbed, pinched, or melted wires.

4. 4

   Disconnect transmission controller connectors C350 and C353. Measure resistance between cavity 9 of connector C350 and cavity 8 of connector C353 on the wiring harness side. It should be approximately 10 ohms.

1. 1

   Safely Prep the Machine

   Park the tractor on a level surface, engage the park brake, turn off the key switch, and disconnect the battery to prevent electrical spikes.

2. 2

   Locate the Solenoid

   Locate the transmission powershift valve block under the cab. The C1 Clutch Solenoid is specifically identified in the OEM schematic as Connector No. 31 on the Powershift Valve Speed block.

3. 3

   Inspect the Connector

   Disconnect Connector No. 31 from the C1 clutch solenoid. Inspect the terminal pins for corrosion, moisture, or bent pins.

4. 4

   Repair Wiring (If Applicable)

   If the diagnostic resistance test failed, trace the wire back to the TCU and repair the short to battery voltage in the harness.

5. 5

   Replace the Solenoid

   If the wiring harness tests perfectly (approx. 10 ohms to the TCU) but the code persists, the solenoid coil has failed internally. Remove the retaining fastener holding the C1 solenoid in the valve block, extract the solenoid, and install the replacement. Ensure the new O-ring seals are lubricated with clean transmission fluid before seating the new solenoid.

6. 6

   Recalibrate

   Reconnect the battery, clear the inactive fault codes from the TCU, and perform a transmission clutch calibration procedure so the controller can learn the fill time and spring pressure of the new C1 clutch solenoid.