Case IH P41 – Electronic Management Unit (EMU): PTO Fender Switch Relay Short To Ground

The control module has detected that the electrical circuit controlling the relay for the fender-mounted rear Power Take-Off (PTO) switch is shorted directly to the chassis ground, preventing the PTO from engaging properly.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190

1. 1

   Test the PTO fender switch relay operation using a multimeter and a 12V power source to verify if it is stuck or fails to switch continuity

2. 2

   Disconnect the Electronic Management Unit (EMU) Connector C105 to isolate the circuit

3. 3

   Use a multimeter to check wire C105-12 (Orange/Light Green wire) for a short to ground with the relay removed and EMU disconnected

4. 4

   Visually inspect the wiring looms running under the cab, under the seat, and out to the rear fenders for broken wires, chafing against moving parts, or corroded connectors

1. 1

   Safety First

   Park the tractor on a level surface, turn off the engine, and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Relay Replacement

   Locate the PTO relay in the main electrical panel. If your diagnostic check in Step 1 failed, plug a new OEM relay into the socket.

3. 3

   Wiring Repair

   If the relay is functional but wire C105-12 showed a short to ground, trace the Orange/Light Green wire from the EMU to the fender switch and relay block.

4. 4

   Fix the Short

   Once the chafed or melted section of the wire is found (commonly near the rear fender where vibration and debris exposure is high), cut out the damaged section. Solder in a new piece of appropriately gauged wire and seal it with heat-shrink tubing.

5. 5

   Reassembly

   Reconnect the EMU C105 connector, plug the relay back in, and reconnect the battery.

6. 6

   Testing

   Turn the key on and clear any stored codes (disconnecting the battery may have already achieved this, though an EST diagnostic tool may be required for hard codes). Test the PTO engagement using both the cab switch and the fender switch to ensure normal operation.