Kubota E-42 – Engine Control Unit (ECU): ACU communication trouble

The main Engine Control Unit (ECU) has lost CAN bus communication with the Aftertreatment Control Unit (ACU). This causes the tractor to immediately enter limp mode, limiting output to approximately 50%, speed/accelerator to 10%, stopping EGR, and opening the intake throttle to 100%.

• M5-091
• M5-111
• M5N-091
• M5N-111
• M6-101
• M6-111
• M6S-111
• M100X
• SVL95-2S
• SVL95-2SC
• TL12V2

1. 1

   Check battery voltage, as low voltage can cause false communication drops (normal voltage is a precondition for this DTC)

2. 2

   Inspect the CRS (main), CRS 2, and ACU relays under the hood for corrosion, moisture intrusion, or damage

3. 3

   Inspect the CAN bus communication wiring harness between the ECU and the ACU for chafed wires, broken pins, or rodent damage

4. 4

   Check fuses to verify that no fuses supplying power to the ACU or dash have blown

1. 1

   Disconnect Power

   Always disconnect the negative battery terminal before servicing the tractor's electrical system or ECU/ACU components.

2. 2

   Relay Replacement

   If the ACU relay under the hood shows signs of moisture, corrosion, or fails a continuity test, replace it with a new 12V 4-pin relay.

3. 3

   Harness Repair

   If a broken wire is found on the ECU-ACU communication harness, repair the wire using proper weatherproof splicing techniques, or replace the affected harness section if the damage is extensive.

4. 4

   Clean Connections

   Disconnect the plugs at both the ECU and ACU. Use electrical contact cleaner to remove any dust or light corrosion. Ensure the pins are straight and firmly seat the connectors back into the modules.

5. 5

   Clear the Code

   Reconnect the battery. The system is designed to recover from this error upon a 'Key switch turn OFF' and subsequent restart once the physical connection is restored.