New Holland NH 4042 – Arm Rest Module (ARU): Arm Rest Module (ARU) CAN 'Bus off'

This is a critical communication fault indicating that the main Arm Rest Module (ARU) has completely lost communication with the vehicle's Controller Area Network (CAN) bus. When a module goes 'Bus off,' it stops transmitting and receiving data to protect the rest of the network from corrupted signals. As a result of this fault, all armrest functions will be disabled.

• New Holland T-Series (T, TL, TLA, TS, TSA, T5000, T6000, T7000, T8 series)
• New Holland TM Series (e.g., TM 175)
• New Holland TVT Series

1. 1

   Check supply voltage for the ARU, including battery, alternator, and power/ground circuits (look for related codes NH 4040 or NH 4041)

2. 2

   Inspect the CAN bus wiring harness connecting the ARU to the main vehicle CAN bus for physical damage, chafing, or pinched wires

3. 3

   Inspect the main connectors at the Arm Rest Module for corrosion, backed-out pins, or moisture intrusion

4. 4

   Look for accompanying codes indicating CAN timeouts or missing modules (e.g., NH 14904 'Arm Rest Module missing')

1. 1

   Power Down

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

2. 2

   Harness & Connector Repair

   Access the Arm Rest Module (ARU) wiring harness. Disconnect the main plug and inspect the pins. Clean any corrosion using electrical contact cleaner. If any wires in the CAN High or CAN Low lines are broken or shorted to ground, splice and repair the wiring according to OEM standards.

3. 3

   Voltage & Ground Test

   Reconnect the battery and turn the key to the ON position. Use a multimeter to verify that the ARU is receiving steady operating voltage (12V nominal) and has a solid ground.

4. 4

   CAN Bus Resistance Test

   With the battery disconnected, measure the resistance across the CAN High and CAN Low pins at the ARU connector. A healthy CAN bus should read approximately 60 ohms. If it reads 120 ohms, a terminating resistor or network wire is broken.

5. 5

   Module Replacement

   If the wiring, voltage, ground, and CAN resistance all test within normal limits but the NH 4042 code persists and the armrest remains unresponsive, the Arm Rest Module (ARU) has suffered an internal hardware failure and must be replaced.