Case IH 3734 – Engine Control Unit (ECU) / CNH EDC: PTO switch : Diagnostic fault check non plausibility of COM message.

The control module is receiving an implausible signal or conflicting data over the CAN bus (COM message) regarding the state of the Power Take-Off (PTO) switch. The system cannot determine whether the PTO switch is legitimately in the ON or OFF position due to a signal error, which typically points to a failure within the switch itself, a wiring harness issue, or a communication breakdown on the CAN network.

• Magnum Series (220, 250, 380)
• Puma Series (115, 125, 140, 155, 165 CVT, 180 CVT)
• Maxxum / MXU Series (110, 115, 125, 135, 140, 150)
• Farmall Series (95U, 105U, 115U, 120U)
• MXM Series (120, 130, 140, 155)

1. 1

   Inspect the PTO switch on the operator console for physical damage, sticking, or fluid intrusion.

2. 2

   Disconnect the PTO switch and inspect the electrical connector and wiring harness for corrosion, backed-out pins, or chafing.

3. 3

   Use a multimeter to test the switch for proper continuity in both the engaged and disengaged positions.

4. 4

   Check the CAN bus communication lines at the switch connector for proper voltage (typically ~2.5V on CAN High and CAN Low) and ensure there are no shorts to ground or battery voltage.

5. 5

   Connect the Case IH EST to monitor the live parameter status of the PTO switch. Check if the ECU registers the switch state changes or if the signal drops out.

1. 1

   Power Down

   Turn off the tractor, remove the key, and ensure the machine is in a safe state.

2. 2

   Access the Switch

   Locate the PTO switch on the right-hand armrest or side console. Depending on the model, you may need to carefully pry up the console trim panel to access the underside of the switch.

3. 3

   Disconnect

   Unplug the electrical wiring harness connector from the bottom of the PTO switch.

4. 4

   Remove the Switch

   Depress the retaining tabs on the sides of the switch body or unscrew the retaining collar (if equipped) to push the switch up and out of the console panel.

5. 5

   Install the New Switch

   Snap the new OEM PTO switch into the console panel until it seats firmly.

6. 6

   Reconnect

   Plug the electrical harness connector back into the switch, ensuring the locking tab clicks into place.

7. 7

   Clear Codes & Test

   Turn the ignition on, use the Case IH EST to clear fault code 3734, and test the PTO engagement/disengagement to verify the repair.