New Holland UCM 1902 – UCM: Power Supply: UCM Supply Voltage LOW

The primary input voltage feeding the control module has dropped below the acceptable operational threshold.

• L213
• L216
• L218
• L220
• L225
• L228
• L230
• L318
• L328
• L330
• L334
• C227
• C232
• C238
• C327
• C332
• C334
• C337
• C345

1. 1

   Check the machine's battery voltage to ensure it is fully charged and holding proper voltage under load.

2. 2

   Check the alternator output (B+ and D+ terminals) to ensure the system is charging properly during operation.

3. 3

   Inspect the main wire harnesses connecting to the UCM for any chafing, pinched wires, corrosion, or loose connector pins.

4. 4

   Check the UCM ground connections for high resistance or corrosion. A poor ground can simulate a low voltage condition.

5. 5

   Inspect the main power supply circuits, fuses, and relays feeding the UCM to ensure there is no voltage drop across the contacts.

1. 1

   Monitor Live Data

   Operate the machine while monitoring the instrument cluster display for live voltage readings.

2. 2

   Repair Wiring

   If physical damage to the wiring harness or connectors is found during the diagnostic checks, repair the damaged wiring or replace the affected harness section.

3. 3

   Clean Connections

   Clean and tighten all battery terminals, alternator connections, and UCM ground points.

4. 4

   Clear and Retest

   If no physical damage is found and the display indicates normal voltage readings after checking connections, erase the fault code using the electronic service tool (EST) or the cab display panel. Resume operation to verify if the code returns.

5. 5

   Module Replacement

   If the voltage supply reaching the UCM connector is verified as good with a multimeter (e.g., a steady 12V+), but the UCM continues to log the 1902 internal low voltage fault, the UCM itself has likely suffered an internal hardware failure and must be replaced.