Case IH FBB – Transmission Controller: Clutch B Solenoid Over Voltage

The transmission controller has detected an abnormally high voltage or a short-to-power (B+) on the electrical circuit that controls the Clutch B solenoid valve, resulting in a loss of drive or missing gears.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190

1. 1

   Verify system voltage to ensure the tractor's alternator is not overcharging, which can trigger over-voltage codes across multiple solenoids.

2. 2

   Inspect the wiring harness between the transmission controller and the Clutch B solenoid for rubbed-through insulation that could be shorting the circuit to a 12V power source.

3. 3

   Remove the cab floor access panel and inspect the transmission connectors (e.g., connector C162 to Clutch B) for water ingress, corrosion, or bent pins.

4. 4

   Disconnect the Clutch B solenoid and measure the resistance across the solenoid pins with a multimeter to check for an internal short.

1. 1

   Preparation

   Park the tractor on a level surface, engage the parking brake, turn off the engine, and remove the key.

2. 2

   Access the Valve Block

   Remove the cab floor mat and access panel (or access the side of the transmission housing, depending on the specific MXM model) to reach the transmission control valve block.

3. 3

   Disconnect

   Unplug the electrical connector from the Clutch B solenoid.

4. 4

   Removal

   Remove the retaining bolt or bracket holding the solenoid in the valve block. Carefully pull the solenoid cartridge out. Have a rag ready, as a small amount of transmission fluid will leak out.

5. 5

   Installation

   Lubricate the O-rings on the new solenoid with clean transmission fluid. Insert the new solenoid into the valve block and torque the retaining bolt to OEM specifications.

6. 6

   Reconnect

   Plug the electrical connector back into the new solenoid.

7. 7

   Clear Codes

   Turn the key on and use the tractor's H-Menu (or a dealer diagnostic tool) to clear the FBB fault code.

8. 8

   Calibration

   Warm the transmission oil to at least 10°C (preferably normal operating temperature) and run the automated clutch calibration sequence so the controller can learn the new Clutch B fill times.