Case IH 518150-03 - BCM – BCM: Electrical crank power relay - short circuit to B+ (Battery Positive)

The control module is detecting battery voltage (12V) on the control circuit for the engine's crank power relay (starter relay) when it should not be present. This indicates that the circuit is shorted to a power source, the relay is internally shorted, or the module itself has an internal fault.

• MAGNUM AFS Connect
• Magnum 180 AFS Connect
• Magnum 340 AFS Connect
• Magnum 380 AFS Connect
• Magnum 400 AFS Connect

1. 1

   Locate the crank power relay in the fuse/relay panel and visually inspect the socket for melting, corrosion, or pushed-out pins.

2. 2

   Inspect the wiring harness running between the BCM and the crank power relay for chafed insulation where the control wire might be rubbing against a constant 12V power wire.

3. 3

   Remove the crank power relay and test the control circuit pin at the relay socket with a multimeter. With the ignition ON but the tractor not cranking, it should not have battery voltage (12V indicates a short to B+).

4. 4

   Swap the crank relay with a known good relay of the same type (e.g., a work light relay) to see if the fault code changes or clears, which would indicate an internally shorted relay coil.

5. 5

   If the wiring tests good, disconnect the harness at the BCM and check for voltage on the wire. If the voltage disappears when the BCM is unplugged, the BCM has an internal short.

1. 1

   Disconnect Power

   Disconnect the tractor's battery negative cable to prevent accidental cranking or electrical spikes during repair.

2. 2

   Access the Relay Panel

   Remove the necessary trim panels or rubber liners to access the main fuse and relay block.

3. 3

   Repair Wiring

   If a short to B+ was found in the harness during diagnostics, splice and repair the damaged section of the wire using OEM-approved heat-shrink connectors. Wrap the harness in protective loom.

4. 4

   Replace the Relay

   If the relay was found to be internally shorted or melted, install a new OEM crank power relay into the socket.

5. 5

   Replace the BCM

   If the BCM is internally shorted to power, it must be replaced. Note that installing a new BCM will require a Case IH dealer technician to program and configure the module to the tractor using the EST (Electronic Service Tool).

6. 6

   Clear Codes and Test

   Reconnect the battery, turn the key ON, and clear the inactive fault codes. Attempt to crank the engine to verify the repair.