Case IH U39 – Transmission Control Module (TCU / Transmission ECU): Transmission Synchroniser Did Not Move Toward Reverse Position

The transmission synchroniser did not move toward the reverse position, even when maximum hydraulic pressure was applied. The transmission controller is commanding a shift into reverse, but the feedback sensor (potentiometer) is not detecting the expected physical movement of the synchroniser.

• Maxxum
• MX Series
• Maxxum Series
• Puma Series
• Steiger Series
• Farmall 40-45-50

1. 1

   Check the synchroniser potentiometer signal using a voltmeter in diagnostic mode (H9) to see if it is out of range or unresponsive

2. 2

   Remove the transmission top or side cover and visually watch the synchroniser movement while a shift is commanded to detect mechanical failure or binding

3. 3

   Verify adequate transmission oil pressure is reaching the synchroniser circuit to rule out a general hydraulic failure

1. 1

   Verify Solenoid Wiring

   Check the forward and reverse solenoid connectors. Swap them to their correct positions if they have been accidentally swapped during previous service.

2. 2

   Inspect the Potentiometer

   Check the synchroniser potentiometer and its connector for physical damage. Verify that the potentiometer has not been painted over during production, which can cause sticking or poor readings. Clean or replace if damaged.

3. 3

   Test the Reverse Solenoid

   Test the reverse solenoid for electrical faults or sticking. Replace the reverse solenoid if it is found to be faulty.

4. 4

   Free up the Synchroniser

   If the synchroniser assembly is very tight or sticky, repeating the transmission calibration procedure may help free up the synchroniser.

5. 5

   Diagnose Hydraulic Pressure

   If the synchroniser still does not move and the electronics are sound, diagnose the transmission hydraulic pump and valve block for a 'no oil pressure' condition to the synchroniser shift circuit.