New Holland 1900 – UCM: UCM Power Supply Ground Fault

The Universal Control Module (UCM) has detected a ground fault in its own power supply, indicating that its connection to the chassis ground is compromised. This electrical issue disrupts the proper operation of the UCM and is considered a high-priority error. As a safety precaution, all hydraulics on the machine are typically disabled when this fault is active.

• L218
• L220
• L221
• L223
• L228
• L230
• L234
• C227
• C232
• C234
• C237
• C238
• C245
• T6 Series
• T7 Series
• T6000 Series
• T7000 Series
• CX Series
• CR Series
• LM6.32
• LM6.35
• LM7.35
• LM7.42
• LM9.35

1. 1

   Use a diagnostic service tool to confirm that fault code 1900 is active and check for any other related active fault codes.

2. 2

   Visually inspect all relevant wiring harnesses and connectors for signs of damage, corrosion, bent or dislodged pins, abrasions, or broken wires. Pay special attention to ground connections near the starter or chafed wiring harnesses, which are common on skid steers.

3. 3

   Flex the wiring harnesses to try and reveal any intermittent breaks or shorts in the wiring.

1. 1

   Check for a short to a higher voltage source

   Disconnect the backup alarm connector (X-BKUP-PWR) and the UCM connector (X-CN3B). Using a multimeter, measure the voltage between pin 18 of the UCM connector X-CN3B and the chassis ground. If voltage is present, there is a short to a higher voltage source on the wire between the backup alarm and the UCM. Repair or replace this wire.

2. 2

   Test the UCM operation

   If no voltage was found in step 1, reconnect the UCM connector X-CN3B. With the multimeter, check for voltage between pin 1 of the backup alarm connector (X-BKUP-PWR) and the chassis ground. If the voltage is greater than 8V, the UCM has likely failed and requires replacement. If the voltage is less than 8V, the issue may be intermittent or located elsewhere in the harness.

3. 3

   Final inspection and verification

   If no specific fault is found, carefully re-inspect all related harnesses and connectors. Once a repair has been made (such as fixing a corroded ground or a damaged wire), clear the fault code using a diagnostic tool and verify the resolution by operating the machine. On many New Holland models, the code will clear itself once the underlying issue is fixed.