Massey Ferguson T4185 – Transmission Control Module (TRANS): Issue With Signal From Transmission Mounted Engine Speed Sensor DYNA VT (TRANS)

The controller is receiving erratic, implausible, or missing rotational speed data from the sensor monitoring the engine's input speed at the transmission.

• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• Interim Tier 4 (2012-2015)
• MF 7600 Series
• MF 7700 Series
• 7714
• 7715
• 7716
• 7718
• 7719
• 7720
• 7722
• 7724
• 7726
• MF 6400 Series
• MF 7400 Series
• MF 8400 Series
• MF 8600 Series
• MF 8700 Series
• 6485
• 7490
• 8450
• 8650
• 8727
• 8730

1. 1

   Check the wiring harness leading to the X25 Engine Speed Sensor for chafed wires causing a short circuit (e.g., short to +12V AC) or an open circuit.

2. 2

   Use a diagnostic tool to monitor the live RPM output of the X25 sensor while the engine is running. Look for dropouts or erratic spikes that confirm the inconsistent speed condition.

3. 3

   Verify the transmission hydraulic oil level and condition, as low fluid or heavy contamination can interfere with sensor readings or indicate broader transmission module faults.

4. 4

   Remove the sensor and inspect the magnetic tip for excessive metal shavings or debris, which can distort the signal.

1. 1

   Locate the Sensor

   Identify the X25 Engine Speed Sensor, which is mounted externally on the transmission housing.

2. 2

   Disconnect Power

   Turn off the tractor and disconnect the battery to prevent electrical shorts.

3. 3

   Remove the Sensor

   Unplug the electrical connector from the sensor. Remove the retaining bolt securing the sensor to the transmission housing and carefully pull the sensor out.

4. 4

   Clean the Port

   Wipe the mounting port clean of any dirt or oil to ensure the new sensor seats perfectly flush.

5. 5

   Install the New Sensor

   Insert the replacement sensor, thread the retaining bolt, and tighten to the OEM torque specification.

6. 6

   Reconnect

   Plug the electrical connector back into the sensor harness.

7. 7

   Clear Codes and Test

   Reconnect the battery, use a diagnostic scan tool to clear the T4185 fault code, and test drive the tractor to ensure the transmission shifts smoothly and the code does not return.