Case IH 3997-05 - BCM – BCM: Electrical accessory power relay - open circuit

This code indicates that the control module is commanding the electrical accessory power relay to turn on, but it detects an "open circuit" (no current flow). This means there is a break in the electrical path, which is typically caused by a blown fuse, a disconnected or unseated relay, a failed relay coil, or a broken wire in the harness.

• MAGNUM AFS Connect
• Steiger AFS Connect

1. 1

   Inspect relay seating and socket for corrosion, melted plastic, or pushed-out pins in the power distribution center

2. 2

   Swap the suspect accessory power relay with a known-good relay of the exact same type (e.g., horn or work light relay)

3. 3

   Test relay coil continuity using a multimeter across the coil pins (typically 85 and 86); infinite resistance (OL) indicates a dead relay

4. 4

   Check the wiring harness between the BCM and the relay socket for continuity, chafing, broken, or pinched wires

5. 5

   Verify that the fuses supplying power to the BCM and the accessory relay circuit are intact

1. 1

   Turn off the tractor, remove the key, and disconnect the battery ground cable to ensure safety while working on the electrical system.

2. 2

   Access the main fuse and relay panel.

   Refer to the operator's manual for the exact location on your specific Magnum AFS Connect cab configuration.

3. 3

   Locate the "Electrical Accessory Power Relay".

4. 4

   If the relay failed the diagnostic test: Remove the faulty relay and install a new OEM replacement relay.

5. 5

   If the wiring failed the diagnostic test: Trace the open wire between the BCM output pin and the relay socket.

   Repair the broken wire using OEM-approved weather-sealed splice connectors, or replace the damaged harness section.

6. 6

   Reconnect the battery ground cable.

7. 7

   Turn the ignition key to the ON position. Use the AFS Pro monitor or a diagnostic scan tool to clear the inactive fault codes.

8. 8

   Turn on the cab accessories to verify the circuit is functioning properly and that code 3997-05 does not return as an active fault.