Case IH 520576-03 - BCM – BCM: Battery isolator set - short circuit to B+

The control module has detected battery voltage (a short to B+) on the battery isolator (disconnect switch) circuit where it should not be present.

• MAGNUM AFS Connect
• Magnum 400 AFS Connect
• Magnum 235 through 380
• Steiger
• Quadtrac

1. 1

   Inspect the mechanical battery isolator switch and disconnect its electrical connector to check for internal shorts or corrosion bridging the terminals.

2. 2

   Check the battery isolator relay and fuses. If the isolator is activated improperly, check and change the fuse or relay if necessary.

3. 3

   Inspect the wiring harness between the battery isolator switch (and its relay coil) and the BCM for chafed wires or melted insulation causing the signal wire to short directly to a 12V power source (B+).

1. 1

   Turn the ignition off

   Turn the ignition off and ensure the machine is in a safe state.

2. 2

   Locate the battery isolator switch

   Locate the battery isolator switch (master disconnect switch).

3. 3

   Disconnect the electrical connector

   Disconnect the electrical connector to the battery isolator switch.

4. 4

   Test for short to battery voltage

   Using a multimeter, test the switch terminals and the harness side for a short to battery voltage.

5. 5

   Repair the harness

   If the harness is shorted to power, trace the wire back to the BCM and repair the damaged section of the harness.

6. 6

   Remove the faulty switch

   If the switch itself has failed internally and is bridging the connection to B+, remove the faulty switch.

7. 7

   Install the new switch

   Install the new battery isolator switch and reconnect the electrical connector.

8. 8

   Clear fault codes

   Clear the BCM fault codes and verify that code 520576-03 does not return.