New Holland UCM 1905 – UCM (Universal Control Module): Power Supply: 5VREF1 Sensor Supply Voltage Out of Range

The control module has detected that the 5-volt reference circuit 1 (5VREF1)—which supplies a steady 5 volts to power various sensors on the machine—is operating outside of its expected voltage parameters. This condition is typically caused by a short to ground, a short to a 12V power source, an open circuit in the wiring harness, an internally shorted sensor pulling the voltage down, or an internal failure of the control module itself.

• L213
• L215
• L216
• L218
• L220
• L221
• L223
• L225
• L230
• C227
• C232
• C238

1. 1

   Inspect the wiring harness connected to the UCM (specifically checking connector X-CN1A) for signs of chafing, bare wires, moisture, or corrosion.

2. 2

   Perform a sensor isolation (drop test) by disconnecting the sensors on the 5VREF1 circuit one at a time. Monitor the active fault codes or measure the reference voltage at the connector. If the 5V reference returns to normal after unplugging a specific sensor, that sensor is internally shorted.

3. 3

   Test the 5VREF1 circuit wires for continuity from the UCM to the sensors using a digital multimeter. Check for shorts to ground or shorts to a 12V power source.

4. 4

   Perform a UCM output test by disconnecting the harness from the UCM and measuring the 5VREF1 output pin directly at the module with the key ON. If the UCM is not outputting 5V with nothing connected to it, the UCM itself has failed internally.

1. 1

   Power Down

   Turn off the machine and engage the battery disconnect switch, or disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Resolve Wiring/Sensor Faults

   If the diagnostic checks revealed a shorted wire, repair or replace the affected section of the wiring harness. If a sensor was found to be shorted, replace the sensor.

3. 3

   UCM Replacement (if necessary)

   If the UCM is proven to be faulty (no 5V output): Disconnect the electrical connectors from the UCM. Unbolt the UCM from its mounting bracket. Install the new UCM and secure the mounting hardware. Reconnect the electrical harnesses.

4. 4

   Re-energize and Flash

   Reconnect the battery. Note that a new UCM is shipped blank and must be flashed/programmed with the correct machine software using the New Holland Electronic Service Tool (EST) before the machine will operate.

5. 5

   Clear Codes

   Use the EST to clear the UCM 1905 fault code and verify that it does not return during operation.