3-1

Bus off condition (I/O connections broken)

Allen-Bradley · Logix 5000

What does 3-1 mean?

A 'Bus off' condition is detected, indicating that the connections between the controller and the I/O modules are broken. This prevents communication and operation of connected I/O.

Common Causes

  • Bus off condition
  • The connections between the controller and the I/O modules are broken

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Verify the number of local expansion modules in the project matches the number of modules that are physically installed in the system.

  2. 2

    Verify all mounting bases are locked and I/O modules are securely installed on mounting bases.

  3. 3

    Verify all 1734 POINT I/O modules are configured to use the Autobaud rate.

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Verified technical data. Last updated: March 2026

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