New Holland UCM 1906 – UCM (Universal Control Module): Power Supply: 5VREF3 Sensor Supply Voltage Out of Range

The 5-volt reference circuit #3 (5VREF3), which supplies regulated power to various sensors, is operating outside of its acceptable voltage parameters. This condition is typically caused by a short to ground, a short to battery voltage within the wiring harness, a failed sensor that is shorting the circuit internally, or a failure of the internal 5V regulator inside the control module.

• L213
• L215
• L218
• L220
• L223
• L225
• L228
• L230
• C227
• C232
• C238

1. 1

   Visual Inspection: Inspect the wiring harness running from the UCM to the machine's sensors for chafing, pinched wires, or bare spots that could be shorting to the machine's chassis (ground) or a 12V power source.

2. 2

   Connector Check: Inspect the UCM connectors and sensor connectors for moisture, corrosion, or bent pins.

3. 3

   Sensor Isolation Test: Because multiple sensors share the 5VREF3 circuit, a single internally shorted sensor can pull the entire circuit's voltage out of range. Disconnect the sensors on this circuit one at a time. If the voltage returns to a steady 5.0V (or the active code changes to a different state), the sensor you just unplugged is the culprit.

4. 4

   Harness Continuity Test: With all sensors and the UCM disconnected, use a digital multimeter to check the 5VREF3 wire for continuity to ground or continuity to battery power.

1. 1

   Power Down

   Turn off the machine, engage the parking brake, and disconnect the negative battery cable to prevent electrical spikes during testing.

2. 2

   Isolate the Fault

   Reconnect the battery and turn the key to the ON position (engine off). Using a multimeter, probe the 5VREF3 circuit at the UCM or at a sensor connector.

3. 3

   Unplug Sensors

   Disconnect the sensors on the 5VREF3 circuit one by one. If the voltage normalizes: Replace the faulty sensor that was pulling the voltage down/up. If the voltage remains out of range: Proceed to step 4.

4. 4

   Test the Harness

   Disconnect the battery again. Disconnect the UCM and all sensors on the circuit. Test the harness for shorts. If a short is found, repair the damaged section of the wiring harness or replace the harness.

5. 5

   Replace the UCM

   If the wiring harness tests perfectly fine and all sensors are verified good, but the UCM is still outputting an incorrect voltage on the 5VREF3 pin, the UCM's internal power supply has failed. Replace the UCM.

6. 6

   Recalibrate

   If the UCM is replaced, the new module must be flashed/programmed with the correct software for your specific machine and its attachments.

7. 7

   Clear Codes

   Clear the fault codes and operate the machine to verify the repair.