Case IH 520578-05 - BCM – BCM: Battery isolator reset - open circuit

The control module is attempting to send a signal to the battery isolator relay/switch circuit but is not detecting the expected return voltage or current. This typically means there is a broken wire, a disconnected plug, a blown fuse, or the internal coil of the battery isolator relay has failed and broken continuity.

• MAGNUM AFS Connect
• Magnum 235
• Magnum 250
• Magnum 260
• Magnum 280
• Magnum 290
• Magnum 310
• Magnum 315
• Magnum 340
• Magnum 370
• Magnum 380
• Steiger 385
• Steiger 435
• Steiger 535
• Puma 110 through 215
• Maxxum 110 through 215
• Farmall 60 through 105

1. 1

   Locate the battery isolator relay and visually check for disconnected plugs, loose terminal nuts, or heavy corrosion on the contacts.

2. 2

   Trace the wiring from the battery isolator relay back toward the BCM. Look for chafed wires, pinched harnesses, or rodent damage that would cause a physical break (open circuit).

3. 3

   Using a digital multimeter, test the control terminals of the battery isolator relay for continuity. If the multimeter reads 'OL' (infinite resistance), the internal coil is broken.

4. 4

   Verify that all fuses related to the BCM and the main battery disconnect system are intact.

1. 1

   Power Down

   Turn off the ignition and manually disconnect the main negative battery cable to prevent accidental shorts or sparks.

2. 2

   Access the Component

   Remove any shielding or covers necessary to access the battery isolator relay/switch.

3. 3

   Wiring Repair (If Applicable)

   If the diagnostic checks revealed a broken wire, splice and heat-shrink the wire to restore continuity.

4. 4

   Component Replacement (If Applicable)

   Unbolt the heavy-gauge battery cables from the isolator relay, noting their positions. Disconnect the smaller control wire harness (the circuit communicating with the BCM). Unbolt the faulty isolator relay from its mounting bracket and install the new unit. Reattach the control harness and the heavy-gauge cables. Torque the terminal nuts to OEM specifications to prevent arcing.

5. 5

   Reassembly & Clearing Codes

   Reconnect the main negative battery cable. Turn the key to the ON position. Use the tractor's AFS Pro display or a diagnostic tool (like Jaltest or CNH EST) to clear the stored BCM fault codes.

6. 6

   Functional Test

   Cycle the battery isolator switch/reset function to ensure the BCM registers the closed circuit and the tractor powers up correctly.