B1005 The multiplex integrated control unit lost communication with the relay control module

What does B1005 mean on a Honda?

B1005. The multiplex integrated control unit lost communication with the relay control module. Body features that share that data link may stop working. This Honda-enhanced code applies to Honda and Acura models that use this code.

Common causes of B1005

• Faulty Relay Control Module
• Relay Control Module harness is open or shorted
• Relay Control Module circuit poor electrical connection
• Faulty Multiplex Control Unit Module (MICU)
• Corroded or loose connector pins on the data link

How to fix B1005

1. Confirm the code with a scan tool and check every module on the system for related faults
2. Inspect the connectors at both ends of the data link for corrosion, moisture, and loose pins
3. Test the data link wiring for opens and shorts with a multimeter
4. Repair any damaged wiring or connector before replacing a module
5. Replace the multiplex integrated control unit (MICU) that fails testing, then clear codes and retest

Sources and review

• Last updated 2026-09-26.