Case IH 9151 – UCM (Universal Control Module): Bus-Warn at CAN-Bus No.1

The controller has lost communication on the primary CAN bus network (CAN 1) for more than 5 seconds. The system enters a 'Bus-Off' state because it detects too many communication errors, an open circuit, a short circuit, or a missing termination resistor on the network.

• skid steer
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• Case Excavators
• Steiger series tractors
• Magnum series tractors
• Puma series tractors
• Axial-Flow Combines
• Early Riser Planters
• Farmlift Telehandlers

1. 1

   Connect the Case IH Electronic Service Tool (EST) to read the controller status and identify exactly which modules are offline

2. 2

   Inspect the CAN bus wiring harness visually for rubbing, chafing, or physical damage

3. 3

   Check connectors for moisture, corrosion, or loose pins, which are frequent causes of temporary bus communication loss

4. 4

   Turn the key on and measure the voltage on the CAN data lines (both CAN High and CAN Low should read approximately 2.4V to 2.5V)

5. 5

   Disconnect the battery and measure the resistance across the CAN High and CAN Low pins (should read approximately 60 Ohms; 120 Ohms indicates an open circuit or broken resistor, 0 Ohms indicates a short circuit)

1. 1

   Isolate the Fault

   If the CAN bus voltage or resistance is out of spec, begin disconnecting the modules on CAN-Bus No.1 one at a time.

2. 2

   Monitor the Network

   If the voltage returns to normal (approx. 2.5V) and the other modules come back online on the EST after unplugging a specific module, that disconnected module (or its connector) is the source of the network failure.

3. 3

   Inspect Terminating Resistors

   If the resistance check yielded 120 Ohms, locate the CAN bus terminating resistors. These are often made of a carbon cylinder with a ceramic coating and can easily crack or fracture under heavy machine vibration. Replace any broken resistors.

4. 4

   Repair Wiring/Connectors

   Clean and seal any moisture-compromised connectors. Repair any chafed wiring shorting to ground or power.

5. 5

   Replace Faulty Modules

   If a specific module (such as the UCM) is internally shorted and pulling the bus down, replace the module.

6. 6

   Clear Codes

   Reconnect all components, turn the key on, and use the Case IH EST to clear the fault codes and verify that communication is fully restored.