Case IH 33 – PTO Control Module: 540/1000 PTO Switch and Circuit Fault

Fault code 33 indicates a fault in the 540/1000 PTO switch and its circuit. This switch detects which PTO shaft speed (540 or 1000 RPM) is currently selected and communicates it to the controller so the correct RPM readout is displayed on the tractor's dash.

• MX Maxxum
• MX Maxxum Series
• MX80C
• MX90C
• MX100
• MX100C
• MX110
• MX120
• MX135
• MX150
• MX170

1. 1

   Isolate the 540/1000 switch (to check for an internally shorted switch, a very common failure): Unhook one wire, tape it off, and run the tractor.

2. 2

   Evaluate the switch test result: If the fault clears but the wrong speed is displayed, connect the two wires together. If the dash corrects itself, the switch is shorted.

3. 3

   If the fault remains active with the switch disconnected (indicating a wiring or controller issue): Inspect the wiring harness and PTO controller.

4. 4

   Test the PTO solenoid (to check if the controller is failing to send power): Run a jumper wire directly to the PTO solenoid to see if it engages. CAUTION: The coil is PWM controlled; do not leave connected long or you will burn out the coil.

5. 5

   Inspect the PTO control box (to check for damage from a shorted PTO coil): Open the module and inspect for burnt circuit board traces.

1. 1

   Test the Switch

   Perform the wire-disconnect test mentioned in the diagnostic checks. If the switch is internally shorted, unbolt the small two-stud switch from beside the PTO shaft and install a replacement.

2. 2

   Inspect Wiring

   If the switch is good, use a multimeter to ohm every wire between the PTO switch, the PTO coil, and the PTO control module to check for shorts to ground or broken wires. Repair any damaged harness sections.

3. 3

   Repair or Replace the Control Module

   If the wiring and switch are intact, remove the PTO control module. Open it and inspect the circuit board. If a trace is burned, you can often solder in a jumper wire across the burnt trace to fix the board (highly recommended to add an inline fuse to the wire going to the PTO coil to protect the module). If the board is beyond repair, replace the entire PTO control module.

4. 4

   Recalibrate

   After replacing the switch, coil, or controller, recalibrate the PTO system to ensure proper operation.