Case IH 3870-05 - IMM – IMM (Immobilizer Control Unit): IMM: LF antenna 2 error - auxiliary I/O current below normal

The Immobilizer (IMM) module has detected an open circuit, a broken wire, a disconnected plug, or a failed internal coil inside 'LF Antenna 2', preventing the antenna from drawing the expected electrical current.

• MAGNUM AFS Connect
• Magnum
• Steiger
• Optum
• Puma

1. 1

   Visually inspect LF Antenna 2 housing for physical damage and the wiring harness for chafing, cuts, or corrosion.

2. 2

   Disconnect the LF Antenna 2 and IMM module connectors to check for loose, backed-out, or corroded pins.

3. 3

   Perform a coil resistance test across the LF Antenna pins using a multimeter (should show low resistance; 'OL' indicates internal failure).

4. 4

   Measure the continuity of the wiring harness between the IMM module connector and the LF Antenna 2 connector.

5. 5

   Verify that neither of the antenna wires is shorted to ground or battery voltage.

1. 1

   Power Down

   Turn off the ignition and disconnect the machine's battery to prevent electrical spikes to the IMM module.

2. 2

   Access the Component

   Remove the necessary cab trim panels or covers to access LF Antenna 2.

3. 3

   Wiring Repair (If Applicable)

   If the harness failed the continuity test, repair the open wire using OEM-approved splicing techniques, or replace the affected harness section.

4. 4

   Antenna Replacement (If Applicable)

   If the antenna failed the resistance test, unbolt/unclip the faulty antenna.

5. 5

   Installation

   Install the new LF antenna. Ensure it is mounted in the exact same orientation as the original, as orientation and positioning are critical to the correct functioning of the smart key detection zone.

6. 6

   Reassembly

   Reconnect the electrical connector and reinstall all trim panels.

7. 7

   Power Up & Clear Codes

   Reconnect the battery. Connect the CNH Electronic Service Tool (EST) to the diagnostic port and clear the active 3870-05 fault code.

8. 8

   System Test

   Bring the smart key into the zone covered by Antenna 2 and verify that the machine recognizes the key and authorizes engine start.