Case IH P27 – Electronic Management Unit (EMU) or PTO Controller: PTO Speed Sensor Open Circuit

This fault code indicates a complete loss of electrical continuity in the PTO (Power Take-Off) speed sensor circuit. The sensor is typically a 2-wire permanent magnet sensor that generates an AC signal as the tone wheel teeth move past it. An "open circuit" means the controller is not detecting any resistance or signal return, which is usually caused by a broken wire, a disconnected plug, or an internal failure of the sensor itself.

• MXM
• MXM Series
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• Puma Series
• Magnum Series
• Steiger Series
• Maxxum / MX Series
• MX150
• MX170
• MX80C
• MX90C
• MX100
• MX110
• MX120
• MX135

1. 1

   Visual Inspection: Locate the PTO speed sensor on the rear PTO housing. Inspect the sensor connector and the immediate wiring harness for physical damage, corrosion, or disconnected pins.

2. 2

   Harness Continuity Test: Disconnect the sensor and use a multimeter to check the wiring harness back to the controller. You are looking for an open circuit (broken wire) in the signal line or the ground line.

3. 3

   Sensor Resistance Test: Test the 2-wire sensor itself for internal continuity. If the sensor reads completely open (infinite resistance), the internal coil has failed.

4. 4

   Check for Swapped Connectors: Verify that the PTO Speed Sensor and the PTO Shaft Sensor connections were not accidentally swapped during previous maintenance (which can trigger related PTO circuit faults).

1. 1

   Power Down

   Turn off the tractor, remove the key, and disconnect the battery ground to protect the EMU/PTO controller.

2. 2

   Locate the Sensor

   Locate the PTO speed sensor mounted on the rear PTO housing assembly.

3. 3

   Disconnect

   Unplug the 2-pin electrical connector from the sensor.

4. 4

   Remove the Sensor

   Remove the retaining bolt holding the sensor in place. Carefully pull the sensor straight out of the housing. (Be prepared for a small amount of oil seepage depending on the fluid level and housing design).

5. 5

   Install the New Part

   Lubricate the O-ring on the new sensor with clean hydraulic/transmission oil. Insert the new sensor into the housing and tighten the retaining bolt to OEM torque specs.

6. 6

   Reconnect and Clear

   Reconnect the 2-pin wiring harness. Reconnect the battery.

7. 7

   Test

   Start the tractor, engage the PTO, and verify that the PTO RPMs are accurately displaying on the dash/monitor. Clear the P27 inactive code from the EMU using the tractor's H-Menu or a diagnostic tool.