Case IH 520329-14 - BCM – BCM: CAN Bus A - short circuit between CAN_L and CAN_H lines

The Controller Area Network (CAN) Bus A has a physical short circuit where the CAN Low (CAN_L) and CAN High (CAN_H) communication wires are touching each other. Because CAN networks rely on a differential voltage between these two lines to transmit data, a short between them completely crashes the network, preventing the BCM and other modules on Bus A from communicating.

• MAGNUM AFS Connect
• Magnum 180 AFS Connect
• Magnum 200 AFS Connect
• Magnum 220 AFS Connect
• Magnum 240 AFS Connect
• Magnum 250 AFS Connect
• Magnum 280 AFS Connect
• Magnum 310 AFS Connect
• Magnum 340 AFS Connect
• Magnum 380 AFS Connect
• Magnum 400 AFS Connect

1. 1

   Perform a resistance test with the battery disconnected by measuring the resistance between the CAN_H and CAN_L pins at the diagnostic port or BCM connector. A healthy CAN bus reads exactly 60 ohms; a reading close to 0 ohms confirms a hard short.

2. 2

   Perform harness isolation by disconnecting the CAN Bus A harness at various inline connectors to isolate which segment of the tractor contains the short. Re-measure the resistance after each disconnection.

3. 3

   Perform module isolation by disconnecting the modules on CAN Bus A one by one. If the short circuit (0 ohms) disappears when a specific module is unplugged, that module has an internal short.

4. 4

   Visually inspect the wiring harness for chafing, pinched wires, or melted insulation, particularly where the harness routes near the cab suspension, moving linkages, or hot engine components.

5. 5

   Inspect connectors for moisture ingress or bent pins bridging the terminals.

1. 1

   Power down machine

   Turn off the ignition and disconnect the tractor's battery to prevent electrical damage during testing.

2. 2

   Locate the short

   Using the isolation methods from the diagnostic checks, narrow down the short to a specific harness segment, connector, or module.

3. 3

   Repair wiring harness

   If the short is in the wiring harness (e.g., rubbed through insulation), cut out the damaged section of the CAN_L and CAN_H wires. Solder in new wire and seal it with marine-grade, adhesive-lined heat shrink tubing. Ensure the wires remain twisted (typically 1 twist per inch) to maintain electromagnetic interference (EMI) protection.

4. 4

   Replace terminating resistors or connectors

   If a connector is melted or a terminating resistor has failed and shorted internally, replace the connector or resistor plug.

5. 5

   Replace BCM

   If the short is isolated to the BCM itself, remove the faulty BCM and install the replacement unit. The new BCM will require software flashing via CNH EST upon installation.

6. 6

   Reassemble and clear codes

   Reconnect all harnesses and the battery. Connect the CNH Electronic Service Tool (EST) to clear the inactive 520329-14 fault code and verify that CAN Bus A communication is fully restored.