New Holland UCM 1901 – UCM (Universal Control Module): Power Supply: UCM Supply Voltage HIGH

This condition indicates that the control module is receiving an input voltage that exceeds its maximum operational limit. In 12-volt systems, this is typically triggered when the system voltage spikes abnormally high (often > 15-16V), which is most commonly caused by an overcharging alternator (a failed internal voltage regulator) or a wiring harness shorting to a higher voltage source.

• L213
• L216
• L218
• L220
• L221
• L223
• L225
• L228
• L230
• L234
• L318
• L320
• L323
• L325
• C227
• C232
• C238
• SR130
• SR150
• SR175
• SR200
• SR220
• SR250
• SV185
• SV250
• SV300
• TR270
• TR320
• TV380

1. 1

   Visual Harness Inspection: Inspect the wiring harness running from the alternator and battery to the instrument cluster and UCM. Verify that the harness is free of damage, corrosion, abrasion, or incorrect attachment.

2. 2

   Static Battery Check: Measure the battery voltage with the machine turned off to establish a baseline (should be around 12.6V).

3. 3

   Alternator Output Check: Start the engine and measure the voltage at the battery and directly at the alternator output. If the voltage climbs excessively high while running, the alternator is overcharging the system.

1. 1

   Disconnect Power

   Always disconnect the battery via the disconnect switch or terminal removal before performing electrical repairs to prevent further module damage.

2. 2

   Repair Wiring

   If the diagnostic inspection revealed damaged connectors or a harness shorted to power, repair or replace the affected wiring sections.

3. 3

   Replace Alternator

   If the running voltage was excessively high during the diagnostic phase, the alternator's internal voltage regulator has failed. Replace the alternator.

4. 4

   Test the UCM

   Reconnect the battery, start the machine, and clear the fault codes. If the alternator is outputting correct voltage and the wiring is intact, but the UCM still registers a "Supply Voltage HIGH" fault, the UCM has likely suffered internal hardware damage from the voltage spike and must be replaced.

5. 5

   Flash New Module

   If the UCM is replaced, the new module will need to be flashed/calibrated by a dealer using the CNH Electronic Service Tool (EST) before the machine will operate correctly.