Case IH U21 – Transmission Control Module (TCM): Engine speed lower than 1200 RPM

A calibration error code indicating the engine speed is too low to proceed with transmission calibration. If the engine is physically running at the correct speed, it indicates a communication or sensor failure where the control module is not receiving the engine speed signal.

• Puma/Mid Range Magnum
• Farmall
• Maxxum
• JXC
• MXM
• MXM Series
• Puma Series
• Maxxum Series
• Steiger Series
• TN Series

1. 1

   Verify operator input: Ensure the hand throttle is set to increase the engine speed above 1200 RPM during the calibration procedure.

2. 2

   Check transmission module data: Access the H9 (or HE) diagnostic menu in the transmission module to see if the engine speed is being detected by the controller.

3. 3

   Verify instrument cluster power: Ensure the instrument cluster is receiving power and functioning normally, as the speed signal often routes through it.

4. 4

   Inspect wiring and CAN bus: Check for a broken CAN bus connection or an open circuit in the wiring harness between the engine speed sensor and the instrument cluster (specifically on mechanical engines).

1. 1

   Initiate calibration

   Start the tractor and initiate the transmission calibration procedure.

2. 2

   Increase engine RPM

   Increase the engine RPM to approximately 1200 rev/min using the throttle.

3. 3

   Proceed with calibration

   If the U21 code clears, proceed with the rest of the transmission calibration.

4. 4

   Monitor live data

   If the code persists despite the engine running at the correct speed, enter the H9/HE diagnostic menu on the transmission module to monitor live engine speed data.

5. 5

   Inspect wiring harness

   If the module reads '0 RPM' or an erratic signal, power down the tractor and inspect the wiring harness connecting the engine speed sensor to the instrument cluster and transmission module. Repair any open circuits or shorts.

6. 6

   Test CAN bus

   Test the CAN bus communication lines for continuity.

7. 7

   Replace engine speed sensor

   If the wiring and CAN bus are intact but no signal is generated, remove and replace the engine speed sensor.

8. 8

   Clear code and test

   Once the repair is made, clear the error code and test the system for normal operation by restarting the calibration procedure.