Case IH 520329-03 - BCM – BCM: CAN Bus A - short circuit to B+

The communication lines for the Controller Area Network (CAN) Bus A are shorted directly to battery voltage (B+). When a CAN line is shorted to power, the network voltage is pulled high, preventing the modules on that bus from transmitting or receiving data properly.

• 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

   Stop the engine, remove the key, and disconnect the battery before disconnecting or connecting any electrical connections.

2. 2

   Inspect the electrical system and wiring harnesses for loose connections, frayed insulation, or pinched wires.

3. 3

   Disconnect the modules on CAN Bus A one at a time to isolate the short. If the short to B+ disappears after unplugging a specific module, that module is internally shorted. If the short remains, the fault is in the wiring harness.

4. 4

   Bench test CAN bus terminators by supplying 12 volts to terminal 1 and checking resistance/functionality to ensure they haven't failed and shorted the network.

1. 1

   Disconnect Power

   Ensure the machine is off and the battery is disconnected to prevent further electrical damage.

2. 2

   Locate the Short

   Using a multimeter, trace the CAN Bus A wiring harness starting from the BCM. Look for areas where the CAN wires may have rubbed through their insulation and made contact with a 12V power supply wire.

3. 3

   Repair the Harness

   If a damaged wire is found, repair the frayed insulation or replace the damaged section of the wiring harness.

4. 4

   Replace Faulty Components

   If the wiring is intact but a specific module or CAN terminator is internally shorting the bus to battery voltage, replace the faulty component.

5. 5

   Reassemble

   Reconnect all modules, plug in the battery, and ensure all access doors, panels, and shields are properly reinstalled.

6. 6

   Clear Codes

   Connect a compatible diagnostic tool (such as the Case IH EST or Jaltest diagnostic software) to the tractor's diagnostic port to clear the fault code and verify that the CAN Bus A network is communicating normally.