Case IH 3643 – Engine Control Unit (ECU): Turbine speed - Signal not plausible

The Engine Control Unit (ECU) has detected an issue with the Turbine Speed Sensor. The signal is 'not plausible,' meaning it does not agree with the engine speed or other transmission speed sensors, causing the controller to flag the signal as invalid. The transmission may default to a 'limp-home' mode.

• Steiger series (350 to 600 HP)
• Magnum series (250, 280, 310, 340, and Rowtrac models)
• Farmall series
• Case CE Wheel loaders (821F, 921F, 1221F, 621G)
• Case CE articulated dump trucks

1. 1

   Verify the code is present and active using the CNH Electronic Service Tool (EASY tool)

2. 2

   Inspect the electrical wiring harness and the connector at the turbine speed sensor for corrosion, bent pins, open circuits, or short circuits to ground/battery voltage

3. 3

   Check that the sensor is installed correctly and securely in its mounting pad

4. 4

   Monitor live data for the engine speed sensor, turbine speed sensor, and output speed sensor using the diagnostic tool, looking for erratic readings or drop-offs from the turbine speed sensor

1. 1

   Locate the Sensor

   The turbine speed sensor is typically an inductive sensor located at the top of the transmission housing or on the transmission mounting pad.

2. 2

   Disconnect Power

   Turn off the machine's key switch and disconnect the battery ground to prevent electrical shorts.

3. 3

   Remove the Sensor

   Disconnect the electrical harness connector from the turbine speed sensor. Remove the retaining bolt/bracket securing the sensor to the transmission housing.

4. 4

   Inspect the Port and Sensor

   Pull the sensor out. Because it is a magnetic inductive sensor, check the tip for excessive metal shavings or debris from the transmission, which can distort the signal.

5. 5

   Install the New Sensor

   If the sensor or wiring is faulty, replace the sensor. Lubricate the O-ring on the new sensor with clean transmission fluid, insert it into the port, and secure it with the retaining bolt.

6. 6

   Reconnect and Test

   Reconnect the wiring harness. Reconnect the battery, clear the fault codes using the diagnostic tool, and operate the machine to ensure the transmission shifts normally and the code does not return.