Case IH 4245 - UCM – UCM: Left external fender switch - unexpected value

The control module is receiving an implausible signal from the left external fender switch, typically caused by internal switch corrosion, water ingress, a sticking button, or high resistance in the wiring harness.

• MAXXUM T4E
• VESTRUM CVX
• Magnum Series (e.g., 235-340)
• Puma Series
• Maxxum Series (e.g., 110 EP - 140 EP)
• Farmall U Series

1. 1

   Inspect the left rear fender switch for physical damage, torn rubber boots, or signs of water ingress

2. 2

   Trace the wiring harness from the left fender switch back to the UCM, looking for chafed wires, pinched harnesses, or loose connections

3. 3

   Disconnect the switch and use a multimeter to check for continuity across the switch contacts when pressed and released

4. 4

   Check the harness side for a short to ground (GND) or a short to battery voltage (Vbat)

5. 5

   If a diagnostic tool is available, monitor the live data for the left fender switch to see if the UCM is registering a fluctuating or stuck signal

1. 1

   Power Down

   Turn off the tractor and disconnect the battery to prevent any short circuits during repair.

2. 2

   Access the Switch

   Locate the left external fender switch housing on the rear fender. Remove the retaining screws or clips holding the switch panel in place.

3. 3

   Disconnect

   Unplug the electrical connector from the back of the switch. Inspect the connector pins for green corrosion or pushed-back pins. Clean with contact cleaner if necessary.

4. 4

   Replace

   If the switch failed the multimeter continuity test or is physically damaged, install the new OEM fender switch into the housing.

5. 5

   Reassemble

   Reconnect the wiring harness and secure the switch back into the fender.

6. 6

   Test

   Reconnect the battery, turn the ignition on, and clear the UCM fault codes. Test the external PTO or hitch function to ensure proper operation and verify the code does not return.