Case IH 5144 – UCM: Aux Thumbwheel Axis Pin B Open Or Shorted To Ground

The control module is detecting a voltage anomaly on the "Pin B" signal circuit of the auxiliary hydraulic thumbwheel (located on the joystick). The fault triggers when the module sees that the circuit is either completely open (a broken wire or disconnected plug) or shorted to ground (voltage pulled down to 0V), preventing the auxiliary hydraulics from receiving the correct proportional input signal. This fault triggers a "White" master telltale lamp.

• skid steer
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Inspect the wiring harness exiting the joystick for physical wear, pinch points, or chafing.

2. 2

   Disconnect the joystick harness connector and check for pushed-out pins, corrosion, or moisture inside the connector.

3. 3

   Check for continuity on the Pin B wire from the joystick connector back to the UCM, and test the Pin B wire for a short to ground.

4. 4

   Verify that the thumbwheel switch is receiving its proper reference voltage (typically 5V) and ground. If voltage is present and wiring is intact, the Hall Effect sensor inside the switch has likely failed.

1. 1

   Power down and bleed pressure

   Power down the machine, turn off the battery disconnect switch, and bleed any residual hydraulic pressure.

2. 2

   Open joystick housing

   Carefully open the joystick handle housing. This usually involves removing the screws holding the two halves of the joystick grip together.

3. 3

   Locate switch

   Locate the auxiliary thumbwheel switch at the top of the joystick.

4. 4

   Trace wires

   Trace the switch's pigtail wires down to the junction/connector within the joystick base.

5. 5

   De-pin wires

   Use a pin-removal tool to de-pin the faulty switch's wires from the Metri-pack connector block, noting the exact pinout locations (specifically Pin B).

6. 6

   Remove switch

   Remove the old thumbwheel switch from the joystick housing.

7. 7

   Install new switch

   Seat the new OEM thumbwheel switch into the housing and route the wires down the stalk.

8. 8

   Pin new wires

   Pin the new wires into the connector block in their correct orientation.

9. 9

   Reassemble joystick

   Reassemble the joystick halves, ensuring no wires are pinched in the plastic clamshell.

10. 10

    Clear codes and test

    Reconnect the battery, turn the key on, and use the diagnostic menu or Electronic Service Tool (EST) to clear the UCM fault codes. Test the auxiliary hydraulics for proper proportional function.