New Holland UCM 5121 – UCM: Right Joystick Forward-Back (F-B) Axis - Pin A Short to Power / Short to Ground / Open Circuit

The control module has detected an electrical failure on Pin A of the Right Joystick's Forward-Back axis circuit. The signal is either shorted to a 12V power source, shorted to chassis ground, or has an open circuit. This triggers an Amber priority warning and the machine will default to a 'limp home' ground drive operating mode for safety.

• L213
• L215
• L218
• L220
• L221
• L223
• L225
• L228
• L230
• L234
• L313
• L316
• L318
• L320
• L321
• L323
• L325
• L328
• L330
• L334
• C227
• C232
• C234
• C237
• C238
• C245
• C327
• C330
• C332
• C334
• C337
• C338
• C345
• C362

1. 1

   Visually inspect the wiring harness and connectors between the Right Joystick and the UCM for pinched wires, chafing, corrosion, or backed-out pins.

2. 2

   Perform a Short to Power Test: Turn ignition OFF, disconnect UCM and Right Joystick connectors, turn ignition ON, and measure voltage between Pin A signal wire and chassis ground (must be less than 0.5 V).

3. 3

   Perform a Harness Wiggle Test while measuring voltage or continuity to reveal any intermittent shorts or opens.

4. 4

   Perform a Joystick Sweep Test: Connect a breakout tee or back-probe Pin A and B, turn ignition ON (engine OFF), and move the joystick through its full range. Voltage should change smoothly from approximately 0.55 V to 4.2 V.

1. 1

   Turn the ignition switch OFF and disconnect the negative battery cable before servicing the electrical system.

2. 2

   If the diagnostic checks revealed a voltage greater than 0.5 V on the isolated signal wire, or a lack of continuity, locate the damaged section of the wiring harness. Repair the broken wire or replace the affected harness section.

3. 3

   If the wiring harness and connectors test perfectly (no shorts to power/ground, no open circuits), the fault is internal to the Right Joystick assembly.

4. 4

   Remove the right-hand control console trim to access the joystick base.

5. 5

   Disconnect the electrical connector from the Right Joystick.

6. 6

   Unbolt the faulty joystick assembly and install the replacement unit.

7. 7

   Reconnect the electrical harness, ensuring the locking tab clicks into place.

8. 8

   Reconnect the battery, turn the ignition ON, and use an Electronic Service Tool (EST) to clear the UCM fault codes.

9. 9

   Test the machine in both ISO and H-Pattern modes to confirm full Boom Raise/Lower and Ground Drive functionality without the code returning.