New Holland 1906 – UCM: 5VREF3 Sensor Supply Voltage Out of Range

The Universal Control Module (UCM) has detected that the 5-volt reference power supply designated as '5VREF3' is outside the acceptable range (below 4.8 volts or above 5.2 volts). This stable 5-volt source is sent by the UCM to power various sensors. The fault can be caused by a short to ground, a short to a power source, or an internal failure in a connected component or the UCM itself. This is a 'Red' priority error that disables all hydraulics as a safety measure.

• L220
• SR220
• SR250
• SV250
• SV300
• TR320
• TV380
• C227
• C232
• C238
• L218
• L230

1. 1

   Verify if the fault code is active after starting the machine and wiggle the wiring harness to check for intermittent issues

2. 2

   Visually inspect the wiring and connectors associated with the UCM, the right-hand control handle, and the Universal Joystick Module for damage, corrosion, abrasion, or insecure connections

3. 3

   With the ignition ON, measure the voltage between pin 9 of the UCM connector X-CN1A and chassis ground (normal is 4.8 V to 5.2 V). Below 4.8 V suggests a short to ground or a component dragging the voltage down; above 5.2 V suggests a short to power

1. 1

   Isolate the faulty circuit

   Turn ignition OFF. Disconnect UCM connector X-CN1A and all components on the 5VREF3 circuit (right-hand control handle, Universal Joystick Module). Measure resistance between pin 9 of the UCM harness connector and chassis ground. If resistance is low (under 20,000 Ω), repair the short to ground in the main wiring harness.

2. 2

   Identify the faulty component

   If resistance is high (greater than 20,000 Ω), reconnect the UCM to its harness. Reconnect the disconnected components one at a time, turning the ignition ON after each. The component that causes fault code 1906 to return is the source of the problem.

3. 3

   Check for shorts to power

   If the initial voltage reading was above 5.2 V, inspect the faulty component's connector and associated wiring for contact with a higher voltage circuit wire. Repair damaged wiring.

4. 4

   Replace faulty component or UCM

   Replace the specific component identified as the cause. If the fault persists with all external components disconnected and the harness verified, the UCM may be faulty. Ensure the UCM is programmed with the latest software before replacing it. A temporary replacement of the UCM can confirm if it is the root cause. Clear fault codes and test operation.