Case IH 2171 (191.08) - DEC – Transmission Control Unit (TCU) or Powertrain Control Module (PTA): Transmission Output Speed Sensor 1 and 2 - Plausibility Error

The control software has detected a discrepancy between the two sensor output signals (a difference in frequency or sensors connected backwards/swapped), triggering a critical fault that often results in limited or no transmission function.

• MAXXUM T4E
• VESTRUM CVX

1. 1

   Verify Sensor Signals: Use a diagnostic tool to monitor and compare the live output signals of both Channel 1 and Channel 2 to see which sensor is dropping out or reading erratically.

2. 2

   Check Wiring Orientation: Verify that Transmission Output Speed Sensor 1 and Sensor 2 are not connected backwards or swapped at the harness connectors.

3. 3

   Inspect Harness and Voltage: Check the voltage supply at the output speed sensor plugs. Test for short circuits to ground, open circuits, or damaged pins in the wiring harness between the sensors and the TCU.

4. 4

   Calibration Check: Ensure that both channels are properly calibrated to provide accurate speed readings.

1. 1

   Turn off machine

   Turn the machine's disconnect switch and key start switch to the OFF position.

2. 2

   Locate sensors

   Locate Transmission Output Speed Sensors 1 and 2 on the transmission housing.

3. 3

   Inspect harnesses

   Disconnect the sensor harnesses and inspect the pins for corrosion, moisture, or push-back.

4. 4

   Trace wiring

   Trace the wiring back to the Transmission Control Unit to ensure continuity and verify that Sensor 1 is pinned to the correct TCU inputs and Sensor 2 is pinned to its respective inputs (correcting them if they are swapped).

5. 5

   Replace sensor

   If the wiring is intact and correctly oriented, remove and replace the faulty Transmission Output Speed Sensor(s).

6. 6

   Reconnect harnesses

   Reconnect the harnesses and turn the key start switch to the ON position.

7. 7

   Perform calibration

   Perform a transmission calibration procedure if required by the service manual.

8. 8

   Clear codes and test

   Clear the diagnostic trouble codes. Operate the machine (often required to reach a specific gear or speed, e.g., above third gear for at least 30 seconds) to verify the plausibility error does not return.