New Holland TMF 179 – PTO Controller: The PTO is receiving no frequency from the Shaft Size Sensor on a two speed PTO.

The tractor's PTO is configured as a two-speed system, but when the PTO is switched on, the controller fails to detect any frequency signal from the shaft size sensor.

• T4 Series
• T5 Series
• T6 Series
• T7 Series
• T8 Series
• T9 Series
• MXM/TM Series
• MX Magnum
• TG Series
• Puma
• Optum

1. 1

   Verify Configuration: Ensure the tractor is actually equipped with and configured for a two-speed PTO.

2. 2

   Check for Swapped Connectors: Verify that the wiring connectors for the PTO Shaft Speed Sensor and the PTO Shaft Size Sensor have not been accidentally swapped.

3. 3

   Test Sensor Resistance: Disconnect the PTO Shaft Size Sensor and check the resistance across the sensor pins (should be approximately 3,000 ohms).

4. 4

   Check Wiring Continuity: Inspect the wiring harness between the PTO controller and the PTO shaft size sensor for continuity and ensure there is no short to the chassis ground.

1. 1

   Power Down

   Turn off the tractor, remove the key, and ensure the PTO is fully disengaged.

2. 2

   Locate the Sensor

   Locate the PTO Shaft Size Sensor, which is mounted directly at the rear PTO shaft housing (do not confuse it with the PTO Speed Sensor on top of the transmission).

3. 3

   Inspect the Harness

   Disconnect the sensor's electrical connector. Inspect the pins for corrosion, moisture, or pushed-back terminals. Clean with contact cleaner if necessary.

4. 4

   Test the Sensor

   Measure the resistance of the sensor. If it reads open (infinite resistance), shorted, or significantly out of the 3 K ohm range, the sensor has failed internally and must be replaced.

5. 5

   Replace the Sensor

   Remove the retaining bolt securing the sensor to the housing. Pull the faulty sensor straight out. Lubricate the O-ring on the new sensor with clean hydraulic/transmission oil, insert it into the housing, and tighten the retaining bolt.

6. 6

   Repair Wiring

   If the sensor tested good in Step 4, the fault lies in the wiring harness. Trace the wires back to the PTO controller and repair any breaks, chafing, or shorts to ground.

7. 7

   Clear Codes and Test

   Reconnect the harness, power on the tractor, and clear the stored fault codes. Engage the PTO to verify that the TMF 179 code does not return and that the shaft size frequency is now being detected.