Case IH 639-02 - IMM – IMM: No CAN traffic for 5 seconds

SPN 639 FMI 02 indicates a CAN Bus Communication Error where data is erratic, intermittent, or incorrect. The Immobilizer Module (IMM) has experienced a complete network interruption and has not received any data frames from the CAN bus for a full 5-second timeout period.

• MAGNUM AFS Connect
• Magnum
• Steiger
• Puma
• Farmall
• combines
• loaders

1. 1

   Check battery and voltage during cranking — voltage dropping below 9-10V can cause modules to drop offline

2. 2

   Measure CAN bus voltage on the Yellow and Green wires against CAN ground (should add up to approximately 5 volts)

3. 3

   Inspect the CAN bus wiring harness visually for chafed, cut, or corroded wires

4. 4

   Audit connectors and grounding at the IMM and ECU for moisture intrusion, poor grounding, or bent pins

5. 5

   Check the network termination resistor to ensure it hasn't failed and pulled the bus down

1. 1

   Stabilize Power

   Verify battery health, alternator output, and clean all primary battery ground connections to ensure stable voltage to the modules.

2. 2

   Isolate the IMM

   Locate the Immobilizer Module (IMM). Disconnect the harness and inspect the pins for water intrusion or overheating.

3. 3

   Test the Harness

   Perform a continuity test on the CAN Yellow and CAN Green wires between the IMM and the main diagnostic port/ECU. Repair any broken wires using approved CAN bus wiring repair connectors.

4. 4

   Seal and Protect

   If moisture was found, dry the connectors, apply dielectric grease, and ensure connector sealing is intact to prevent future water intrusion.

5. 5

   Software Update

   Ensure the tractor's controllers (including the TECU and IMM) are updated to the most current software version, as outdated software can cause ISO/CAN communication drops.

6. 6

   Clear Codes

   Connect the Case IH Electronic Service Tool (EST) via the protocol adapter to clear the fault codes and monitor live CAN bus parameters to ensure traffic has resumed.

7. 7

   Module Repair/Replacement

   If the wiring and voltages are perfect but the IMM still cannot communicate, the module itself has likely suffered an internal hardware failure (such as a blown CAN transceiver) and must be repaired or replaced.