Case IH F21 – Transmission Control Unit (TCU): Transmission Extension Harness To Main Harness Disconnected

The transmission extension harness to the main harness is disconnected, causing the transmission to become completely inoperable.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• MX/TG Series

1. 1

   Visually inspect the connection point between the main wiring harness and the transmission extension harness.

2. 2

   Check the wiring and connections going directly to clutch solenoids C, D, and E, as well as the synchronizer solenoids.

1. 1

   Locate the Harness Junction

   Find the connection where the transmission extension harness plugs into the main tractor harness.

2. 2

   Inspect and Reconnect

   Check the connectors for physical disconnection, corrosion, or pushed-out pins. Clean the terminals if necessary and firmly reconnect the harness.

3. 3

   Clear and Retest

   Turn the machine on to see if the F21 code clears and transmission function is restored.

4. 4

   Inspect Solenoids

   If the code persists, trace the extension harness down to the transmission housing. Inspect the individual connectors at clutch solenoids C, D, and E, and the synchronizer solenoids.

5. 5

   Continuity Testing

   Test the extension harness for internal breaks or shorts. If the wiring is damaged internally, the harness will need to be repaired or replaced.