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
Verify the number of local expansion modules in the project matches the number of modules that are physically installed in the system.
- 2
Verify all mounting bases are locked and I/O modules are securely installed on mounting bases.
- 3
Verify all 1734 POINT I/O modules are configured to use the Autobaud rate.
Verified technical data. Last updated: March 2026
Related Faults
Source: Logix 5000