Case IH 81 – Tractor Multi-Function (TMF) Controller, FNR-PTO Controller, Transmission Control Module (TCM), or ECM: Auto PTO switch is open / Valve spool cannot be returned to neutral / Transmission hydraulic oil pressure switch short to ground or open

The PTO controller detects an open circuit from the PTO switch for an extended period when a closed circuit is expected. Alternatively, a hydraulic valve spool is mechanically stuck (MXM Series), or the ECM detects a short to ground or open circuit between the Transmission Pressure Switch and the ECM connector (TN Series).

• MX Maxxum
• MXM120
• MXM130
• MXM140
• MXM155
• MXM175
• MXM190
• Magnum MX Series
• Maxxum MX Series
• Puma Series
• Maxxum Series
• Farmall Series
• TN Series
• CX Series

1. 1

   For PTO switch faults: Check the PTO switch connector to ensure no pins are pushed back or corroded, and inspect the wiring harness for rodent damage or chafing.

2. 2

   For PTO switch faults: Verify that the PTO controller fuse (often located by the hydraulic levers) is not blown.

3. 3

   For PTO switch faults: Disconnect the PTO switch and use a multimeter to test resistance. The switch should close to ground when the PTO is engaged. If it reads OPEN, the switch has failed internally.

4. 4

   For PTO switch faults: Verify the PTO controller is receiving signals from the alternator (engine RPM) and the output shaft speed sensor. A flashing green indicator light by the PTO switch means the controller is locking out engagement due to a missing signal.

1. 1

   Power Down

   Turn the keyswitch to the OFF position and engage the parking brake.

2. 2

   Access the Switch

   Remove the locating screw or carefully pry the PTO switch housing assembly from the side console/dash.

3. 3

   Disconnect

   Unplug the electrical connector from the suspect PTO switch.

4. 4

   Test Wiring

   With the switch removed, use a jumper wire on the harness side to simulate a closed circuit. If the controller registers the circuit as closed, the wiring is good and the switch is definitively the culprit.

5. 5

   Install New Part

   Connect the new OEM PTO switch to the wiring harness and snap it back into the console housing.

6. 6

   Clear Codes

   Use an electronic service tool (or the tractor's onboard diagnostic display) to clear any logged fault codes, then start the tractor and verify PTO engagement.