Case IH 4256 – Auxiliary Control Unit (ACU) or Electronic Hitch Control (EHR) module: Hydraulic master switch short to Vbat

The controller is detecting continuous battery voltage on the switch's signal line, which typically means the wiring harness has chafed and is touching a live power wire, or the switch itself has failed internally and is bridging the power circuit. This condition will often lock out the Electronic Hitch Control (EHR) and auxiliary hydraulics for safety, forcing the system into 'transport mode'.

• MAXXUM T4E
• VESTRUM CVX
• Puma 130
• Puma 145
• Puma 150
• Puma 160
• Puma 165
• Puma 175
• Puma 180
• Puma 195
• Puma 210
• Puma 225
• Maxxum 110
• Maxxum 115
• Maxxum 120
• Maxxum 125
• Maxxum 130
• Maxxum 140
• Farmall 95U
• Farmall 105U
• Farmall 115U Pro EP

1. 1

   Check the main wiring harness (harness A.30.A) routing from the right-hand armrest/console to the Auxiliary Control Unit (ACU) for pinched or chafed wires shorting to a +12V source

2. 2

   Disconnect the hydraulic master switch and use a multimeter to check for an internal short circuit

3. 3

   Verify the voltage at the switch connector and check the condition of related circuit fuses (e.g., F-051 5A Mini fuse or F-007 20A fuse)

4. 4

   Use the tractor's diagnostic display to check the switch status. If the system reads the switch as constantly 'ON' or in 'transport mode' even when physically toggled, the short is confirmed

1. 1

   Depower the System

   Turn off the tractor, relieve all hydraulic pressure, and disconnect the battery to prevent electrical spikes.

2. 2

   Access the Switch

   Remove the trim panels on the right-hand console or the armrest electronic adjustment control where the hydraulic master switch is housed.

3. 3

   Isolate the Fault

   Unplug the hydraulic master switch. Reconnect the battery temporarily and turn the key to the ON position. Use a multimeter to check the signal wire on the harness side. If it still reads +12V, the short is in the wiring harness. If the voltage drops to 0V, the switch itself is internally shorted.

4. 4

   Repair or Replace

   If the switch is faulty: Replace the hydraulic master switch with a new OEM unit. If the harness is faulty: Trace the wire back to the ACU, locate the chafed section shorting to power, repair the wire with solder and heat-shrink tubing, and re-loom the harness.

5. 5

   Reassembly and Clearing

   Reconnect the switch, reassemble the console panels, and clear the fault codes via the tractor's diagnostic menu. Test the EHR and auxiliary hydraulics to ensure full functionality.