Case IH 4042 – Arm Rest Module (ARU): Arm Rest Module (ARU) CAN 'Bus off'

The main armrest controller has completely lost communication with the vehicle's Controller Area Network (CAN) bus. The tractor's ECU cannot send or receive messages from the armrest, and all armrest-controlled functions (such as hydraulics, PTO, and transmission shifting) will be disabled.

• Maxxum
• Puma Series (140, 165, 175, 180, 195, 210)
• Magnum Series (MX180, MX210, MX240, MX285, 235-340)
• Steiger Series (280, 330, 450, 535, 540)
• Maxxum Series

1. 1

   Verify the power and ground voltage supply to the ARU (look for accompanying codes 4040 or 4041).

2. 2

   Inspect the main wiring harness connecting to the armrest for pinched wires in pivot points, backed-out pins, or corrosion.

3. 3

   Use a multimeter to check CAN High and CAN Low lines for continuity, shorts to ground, or shorts to power.

4. 4

   Check the CAN bus terminating resistors (typically 60 ohms across the network when powered down).

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the battery to prevent electrical spikes during repair.

2. 2

   Repair Wiring

   If the diagnostic checks revealed a broken wire or short in the armrest pivot harness, splice and repair the damaged CAN or power wires. Reconnect and test.

3. 3

   Clean Connections

   If the wiring is intact but connectors are dirty, clean the ARU harness connectors with electrical contact cleaner and apply dielectric grease.

4. 4

   Replace the ARU

   If the wiring, terminating resistors, and voltage supply are all within spec, the Arm Rest Module (ARU) has likely suffered an internal hardware failure and must be replaced.

5. 5

   Reprogram/Calibrate

   Installing a new or remanufactured ARU requires a dealer diagnostic tool (such as the Case IH EST or Jaltest) to flash the correct software parameters for your specific tractor configuration and to calibrate the armrest potentiometers and switches.