Case IH 6912-16 - DEC – Transmission Control Unit (TCU): Transmission hydro motor speed sensor data valid, above normal range - moderately severe

The Transmission Control Unit (TCU) is receiving a valid frequency signal from the hydro motor speed sensor, but the reported speed of the hydrostatic motor is higher than the expected or safe operating range. This can indicate that the sensor is reading an actual overspeed condition (potentially due to internal transmission slippage, cavitation, or a mechanical issue in the CVT planetary drive) or that the sensor itself is failing and outputting an artificially high reading.

• MAGNUM AFS Connect
• Magnum CVT series
• Magnum 340 CVT
• T8.275
• T8.300
• T8.330
• T8.360
• T8.385
• T8.390
• T8.420

1. 1

   Inspect the 2-pole female connector (X-074) and the wiring harness leading to the hydro motor speed sensor for chafing, corrosion, or loose pins.

2. 2

   Remove the sensor and inspect the magnetic tip for metal debris. An accumulation of metal shavings can distort the magnetic field, causing erratic or falsely high frequency readings. If heavy metal debris is found, it may indicate a severe internal mechanical failure in the hydrostatic unit.

3. 3

   Verify the sensor is seated fully and securely mounted. An improperly gapped sensor can cause abnormal signal frequencies.

4. 4

   Use a diagnostic tool to monitor the live hydro motor speed while driving. Compare it against engine RPM and wheel speed to determine if the sensor's output is physically plausible or if it spikes erratically.

5. 5

   Restart the vehicle to see if the code is an active hard fault or an intermittent glitch. If the error persists, proceed with sensor replacement.

1. 1

   Preparation

   Park the tractor on a level surface, engage the parking brake, turn off the engine, and disconnect the battery to prevent accidental short circuits.

2. 2

   Locate the Sensor

   Locate the hydro motor speed sensor on the CVT transmission housing. It is typically protected by a bolt-on access cover.

3. 3

   Remove the Access Cover

   Unbolt and remove the hydro motor speed sensor access cover (Part # 47624853).

4. 4

   Disconnect the Harness

   Carefully unplug the 2-pole electrical connector from the sensor.

5. 5

   Remove the Sensor

   Remove the retaining bolt(s) securing the sensor to the transmission housing and pull the sensor straight out.

6. 6

   Install the New Sensor

   Lubricate the O-ring on the new sensor with clean transmission fluid. Insert it into the port and tighten the retaining bolt to the OEM specified torque.

7. 7

   Reassembly

   Reconnect the electrical harness, ensuring the locking tab clicks into place. Reinstall the access cover.

8. 8

   Calibration/Testing

   Reconnect the battery, clear the fault codes using a diagnostic tool, and perform a test drive to verify that the hydro motor speed remains within the normal operating range and the code does not return.