Case IH 2161 (519174.04) - DEC – Transmission Control Module (TCM): Synchro 6-8 Position Sensor - open circuit or short circuit to GND

The control module has detected an electrical fault (an open circuit or a short circuit to ground) in the circuit for the Synchro 6-8 position sensor. When the signal voltage drops below the expected range or is lost entirely, the controller cannot verify the position of the synchronizer, which can result in shifting issues or a disabled transmission.

• MAXXUM T4E
• MXM120
• MXM130
• MXM140
• MXM155
• MXM175
• MXM190
• Maxxum Series
• Puma Series

1. 1

   Visually inspect the transmission wiring harness (specifically the synchro position sensor loom) and the sensor connector for corrosion, backed-out pins, or wire chafing that could cause an open or short to ground.

2. 2

   Back-probe the sensor to check the signal voltage and compare the readings against a known good sensor on the transmission.

3. 3

   Perform 'Swapnostics' by swapping the suspect Synchro 6-8 sensor with another accessible sensor (such as the Forward/Reverse synchro sensor). Clear the codes and run a quick transmission calibration. If the fault code moves to the new location, the sensor has failed internally. If the fault code remains on the Synchro 6-8 circuit, the issue is in the wiring harness or the TCM.

1. 1

   Access the Sensor

   Locate the Synchro 6-8 position sensor on the transmission housing/top plate.

2. 2

   Removal

   Disconnect the electrical connector from the sensor. Remove the retaining hardware (typically a circlip/snap ring or small mounting bolts) and carefully pull the rotary sensor off the synchronizer shaft.

3. 3

   Installation

   Install the new rotary position sensor onto the shaft, ensuring the internal tangs align correctly with the synchronizer linkage. Secure it with the retaining hardware.

4. 4

   Reconnect

   Plug the wiring harness connector back into the sensor.

5. 5

   Calibration

   You must perform a transmission calibration after replacing the sensor. This allows the TCM to learn the minimum and maximum voltage values (the sweep) of the new potentiometer so it knows exactly where the synchronizer fork is during shifts.