Case IH 1979-04 - UCM – UCM: Rear pilot head #6 reporting supply voltage low

While 1979-04 is not a valid code, an actual UCM low voltage fault (like 1902) means the Universal Control Module is receiving insufficient voltage to operate correctly. This is typically caused by a dying battery, a failing battery disconnect switch, or poor ground connections.

• MAGNUM AFS Connect
• Alpha Series skid steers
• B Series skid steers
• TV450B
• compact track loaders

1. 1

   Test the main battery voltage. A reading of 10.99V or lower is insufficient and will trigger UCM voltage faults.

2. 2

   Inspect the battery disconnect/kill switch for loose terminals or internal faults. Bypassing the switch temporarily can help determine if it is the source of the voltage drop.

3. 3

   Check the UCM power supply circuits and ground connections for shorts or open circuits.

1. 1

   Test battery voltage

   Disconnect the battery and test its resting voltage.

2. 2

   Clean and tighten terminals

   Clean and tighten all battery terminals.

3. 3

   Inspect battery disconnect switch

   Inspect the battery disconnect switch. If the switch is faulty, remove the cables and place them together on a single bolt to bypass the switch, or replace the switch entirely.

4. 4

   Reconnect battery and verify

   Reconnect the battery and verify that the UCM supply voltage fault codes have cleared.