12-34

Keyswitch mismatch after switchover

Allen-Bradley · Logix 5000

What does 12-34 mean?

Immediately after a switchover, the keyswitch positions of the primary and secondary controllers are mismatched. Specifically, the old primary is in Program mode and the new primary is in Run mode.

Common Causes

  • Keyswitch positions of primary and secondary controllers mismatched after switchover
  • Old primary controller in Program mode, new primary in Run mode

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Change the keyswitches from Run to Program to Run mode twice to clear the fault.

  2. 2

    Use the Logix Designer application to go online with the controllers, then clear the faults and change both the controllers' modes to Run.

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Verified technical data. Last updated: March 2026

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