How to Reset Allen-Bradley PLC: Quick Solutions

1. Understanding When to Reset an Allen-Bradley PLC

A reset is typically needed when:

• The PLC is in fault mode (solid red fault light).
• A major fault error occurs, requiring a power cycle.
• You need to restore default settings for reprogramming.
• The system is unresponsive or misbehaving.

2. Methods to Reset an Allen-Bradley PLC

Method 1: Power Cycle (Basic Reset)

A simple power cycle can clear minor issues and restore normal operation.

1. Turn OFF the PLC’s power supply.
2. Wait 10–30 seconds for capacitors to discharge.
3. Turn the power ON and observe the status lights.

If the issue was minor, the PLC should restart normally.

Method 2: Fault Reset via Programming Software (RSLogix/Studio 5000)

For more serious faults, you’ll need to reset the PLC using software like RSLogix 500 (for older models) or Studio 5000 (for newer CompactLogix/ControlLogix PLCs).

1. Connect to the PLC via Ethernet or serial cable.
2. Open RSLogix 500 / Studio 5000 and go online.
3. Navigate to Controller Properties > Faults tab.
4. Click “Clear Faults” to reset the error.
5. Set the PLC mode back to RUN or REMOTE RUN.

The PLC should now be operational.

Method 3: Memory Reset (Factory Reset for Hard Faults)

If a PLC remains unresponsive or you need to restore factory settings, perform a full memory reset.

1. Turn OFF the PLC.
2. Locate the Memory Reset Switch (varies by model).
3. Hold the switch in the reset position while turning the power ON.
4. Wait for the status LEDs to flash, then release the switch.
5. Reconfigure the PLC as needed.

Warning: This erases all stored programs! Ensure backups are available before proceeding.

Method 4: Reset Using a Physical Key Switch (For Models with a Key Switch)

Some Allen-Bradley PLCs (e.g., ControlLogix) have a key switch with modes:

• RUN – Executes the program
• REM – Remote access mode
• PROG – Stops the program

1. Turn the key switch to PROG mode.
2. Wait a few seconds, then turn it back to RUN.
3. Check if the fault clears.

A quick and effective way to reset without software.

3. Additional Troubleshooting Tips

• Check the error code: The PLC’s status lights or software logs can help diagnose issues.
• Verify I/O connections: Faults can result from disconnected or malfunctioning inputs/outputs.
• Update firmware if needed: Older firmware versions may cause unexpected faults.
• Replace battery if applicable: Some PLCs require a functioning battery for memory retention.

Final Thoughts

Resetting an Allen-Bradley PLC is a straightforward process when you follow the correct steps. Whether using a simple power cycle, software reset, or full memory reset, always ensure you have a backup of your PLC program before performing any major actions.

Need further help? Leave a comment or reach out to a technician for support.