New Holland F91 – Transmission Controller (TCU): Display Of Gears Controller (CAN Dog) Not Present

This fault code indicates a communication failure on the Controller Area Network (CAN) bus. Specifically, the main transmission controller is unable to detect or communicate with the gear display unit (often referred to as the 'CAN Dog') located in the cab.

• New Holland TM115
• New Holland TM120
• New Holland TM125
• New Holland TM130
• New Holland TM135
• New Holland TM140
• New Holland TM150
• New Holland TM155
• New Holland TM165
• New Holland TM175
• New Holland TM190
• New Holland MXM Series
• New Holland TS115A
• New Holland TS135A
• New Holland T6000 Series
• New Holland T7000 Series

1. 1

   Access the gear display unit in the cab and visually inspect the wiring harness and connectors for obvious mechanical damage, corrosion, or loose pins.

2. 2

   Verify that the gear display unit is receiving proper 12V operating power and has a clean ground connection.

3. 3

   Using a digital multimeter, test the CAN High and CAN Low wires between the transmission controller and the gear display unit for continuity.

4. 4

   Test the CAN lines for shorts to ground or shorts to voltage.

5. 5

   Check if other modules are communicating. If multiple CAN-related codes are present, the issue may be a central wiring harness fault rather than the display itself.

1. 1

   Disconnect Power

   Disconnect the tractor's battery to prevent electrical spikes during module handling.

2. 2

   Access the Display

   Remove the interior cab trim panels surrounding the gear display unit (usually located on the right-hand console or instrument cluster area, depending on the exact model).

3. 3

   Remove the Faulty Unit

   Unplug the wiring harness connector from the back of the gear display. Unbolt or unclip the display from its mounting bracket.

4. 4

   Install the New Unit

   Connect the wiring harness to the replacement gear display unit and secure it into the console.

5. 5

   Reassemble and Power Up

   Reinstall the cab trim panels and reconnect the battery.

6. 6

   Clear Codes and Calibrate

   Turn the ignition key to the ON position. Verify that the gear display powers up and the F91 code is no longer active. Depending on the tractor model and software version, you may need to clear stored fault codes and perform a transmission/clutch calibration routine (often accessed by holding the upshift/downshift buttons while starting the engine) to sync the new controller.