Case IH 8035 - UCM – UCM: Front PTO fender switch - input short to 12V

The control module is receiving a continuous 12-volt signal on the PTO fender switch input circuit. This happens when there is a short across fender switch wires (chafed wires touching live power) or the switch has failed internally, bridging the connection.

• VESTRUM CVX
• Case IH Puma series (165, 180, 195, 210, 225 CVX)
• Case IH Maxxum series (Tier 3)

1. 1

   Disconnect the electrical power for all conductors and isolate it before carrying out work on the system.

2. 2

   Inspect the wiring harness routing near the left-hand and right-hand rear fenders (specifically looking at the 'FENDER SWITCH LH - RH LINK' and 'FENDER PTO SWITCH INPUT' circuits) for chafed insulation causing a short across the wires.

3. 3

   Isolate the fault by disconnecting the Front PTO fender switch. Check the connections for corrosion or bridging.

4. 4

   Verify the voltage at the UCM (Pin 35 / AI_09) to see if the short to +12V is present when the switch is unplugged. This confirms a harness issue rather than an internal switch issue.

1. 1

   Shut down the tractor and disconnect the battery power source to prevent electrical injury.

2. 2

   Access the fender switch panel on the affected side (Left Hand or Right Hand rear fender).

3. 3

   Disconnect the electrical connector from the PTO fender switch.

4. 4

   If the diagnostic checks revealed a harness short, locate the damaged section of the wiring harness (referencing the A.30.A Wiring Harness Overview).

   Repair the wire by soldering and applying heat-shrink tubing, then re-secure the harness away from pinch points.

5. 5

   If the switch itself is internally shorted, remove the retaining clips/screws holding the switch to the fender housing and extract the switch.

6. 6

   Install the new PTO fender switch and reconnect the wiring harness.

7. 7

   Restore battery power and clear the error codes from the instrument cluster/UCM memory.