Case IH 3997-03 - BCM – BCM: Electrical accessory power relay - short circuit to B+

The control module is detecting battery voltage (B+) on the accessory power relay circuit at an improper time. This typically means the control circuit is shorted directly to a 12V power source, or there is an internal fault in the relay or module.

• 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
• Steiger AFS Connect

1. 1

   Locate the Electrical Accessory Power Relay in the vehicle's fuse and relay distribution box.

2. 2

   Disconnect the relay and use a multimeter to check the control circuit leading back to the BCM for an unwanted 12V signal (short to B+).

3. 3

   Inspect the wiring harness between the BCM and the relay block. Look for chafed insulation, melted wires, or pinched harnesses that could bridge the relay control wire to a constant or switched battery power wire.

4. 4

   Test the accessory relay itself to ensure it has not failed internally, causing a short.

5. 5

   Inspect the BCM connectors (e.g., X1, X2, X3, X4, X5) for water ingress, corrosion, or bent pins that could be bridging power to the relay circuit.

1. 1

   Disconnect Power

   Disconnect the tractor's battery to prevent further electrical damage during the repair.

2. 2

   Replace the Relay

   If the diagnostic tests reveal the accessory power relay is internally shorted, replace it with a new OEM relay.

3. 3

   Repair the Wiring Harness

   If a short to B+ is found in the wiring, locate the damaged section. Splice in new wiring using proper weather-sealed connectors and re-wrap the harness securely.

4. 4

   Replace the BCM

   If the relay and wiring harness test good, the BCM itself likely has an internal hardware short on that specific driver circuit. Replace the BCM.

5. 5

   Reconfigure the Module

   If the BCM is replaced, you must perform a "WRITE CONFIGURATION" using the dealer diagnostic tool (e.g., EST) to write the specific vehicle configuration files to the new module.

6. 6

   Verify Repair

   Reconnect the battery, clear the inactive fault codes, and cycle the key/accessories to verify that code 3997-03 does not return.