Case IH 4244 - UCM – UCM: Left external fender switch short to Vbat

The control module has detected a 'short to Vbat' (short to battery voltage/12V) on the circuit for the left external fender switch. This is usually caused by a switch that has failed internally (stuck closed), water/dirt ingress bridging the connections, or a wiring harness chafing against a power wire.

• MAXXUM T4E
• VESTRUM CVX
• Magnum Series: 235–340 (Series 4)
• MX Series: MX80C, MX90C, MX100C, MX210, MX230, MX255, MX285
• Puma Series: 140, 145, 160, 210
• Maxxum Series: 110 EP through 140 EP
• Farmall Series: U Series, 85C, 95C, 105C
• Steiger Series

1. 1

   Visually inspect the left rear fender switch for physical damage, sticking buttons, or packed dirt/mud.

2. 2

   Unplug the switch and inspect the connector for water, dirt, or bent pins.

3. 3

   With the tractor off, unplug the UCM connector (e.g., connector 92) and inspect for water or dirt ingress.

4. 4

   Disconnect the fender switch to isolate the circuit. If the fault code changes from a 'short to Vbat' to an 'open circuit' (such as code 1074 or 5006), the switch itself is internally shorted. If the 'short to Vbat' code remains active while the switch is unplugged, the wiring harness is shorted to a 12V source somewhere between the fender and the UCM.

5. 5

   Verify the UCM supply voltages and related fuses (such as the 12VF3 voltage supply or the 15A EHR/Armrest fuses) to ensure a blown fuse isn't causing erratic module behavior.

1. 1

   Power Down

   Turn off the tractor and disconnect the battery to prevent electrical spikes.

2. 2

   Access the Switch

   Locate the left external fender switch on the rear fender assembly.

3. 3

   Remove the Switch

   Unclip or unbolt the switch housing from the fender and disconnect the wiring harness pigtail.

4. 4

   Test/Replace the Switch

   If diagnostic checks proved the switch was internally shorted, install the new OEM replacement switch.

5. 5

   Harness Repair (If Applicable)

   If the fault is in the wiring, trace the harness from the left fender back to the UCM. Look for areas where the wire loom rubs against the chassis or exhaust components. Splice and heat-shrink any exposed wires that are shorting to power.

6. 6

   Reassembly

   Secure the wiring using OEM clips (e.g., part 47505757) to prevent future chafing. Reconnect the battery.

7. 7

   Clear Codes

   Power up the tractor and verify that the UCM no longer displays the fault code.