🛠️ How to Reset an Allen-Bradley PLC (MicroLogix, CompactLogix, Contro
Whether you’re troubleshooting a solid red fault light or restoring a PLC to factory settings, knowing how to properly reset your Allen-Bradley controller can save valuable time and prevent unnecessary downtime. This guide breaks down four effective reset methods—along with when and how to use them.
🧭 Quick Reset Method Selector
| Scenario | Best Reset Method |
|---|---|
| Minor issue or temporary glitch | Method 1: Power Cycle |
| Major fault but PLC is still responsive | Method 2: Software Reset |
| Total system freeze or memory wipe needed | Method 3: Factory Reset |
| Need a quick hardware-based reset | Method 4: Key Switch |
🔍 1. When Should You Reset an Allen-Bradley PLC?
You may need to reset the PLC if:
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A solid red fault LED is on
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A major fault has occurred
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The PLC is unresponsive or stuck
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You’re about to reprogram and want to start clean
🔄 2. Reset Methods Explained
✅ Method 1: Power Cycle (Basic Reset)
Best for minor runtime issues or simple glitches.
Steps:
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Turn OFF power to the PLC.
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Wait 10–30 seconds to let capacitors fully discharge.
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Turn power back ON.
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Check LED indicators—if the issue was minor, the PLC should reboot normally.
💡 Tip: Keep this method as your first go-to before escalating to software or factory reset.
🧑💻 Method 2: Reset via RSLogix 500 / Studio 5000
Used to clear major or recoverable faults using Allen-Bradley software.
Applies to:
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MicroLogix/SLC (use RSLogix 500)
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CompactLogix/ControlLogix (use Studio 5000)
Steps:
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Connect to the PLC via Ethernet or serial.
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Open RSLogix 500 or Studio 5000, then go online with the controller.
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Navigate to:
Controller Organizer > Controller > Properties > Faults -
Click “Clear Faults”.
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Change the controller mode to RUN or REMOTE RUN.
⚠️ Note: Always investigate the cause of the fault before clearing it to avoid repeat errors.
🧼 Method 3: Factory Reset (Memory Clear / Hard Reset)
For unrecoverable errors, locked-up systems, or when wiping all data is required.
⚠️ Warning: This will erase your program and all memory. Ensure backups are made first.
Steps:
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Turn OFF the PLC.
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Locate the Memory Reset Switch (location varies by model—check your manual).
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Hold the switch in the reset position.
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While holding, turn the power ON.
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Wait for the status LEDs to flash, then release the switch.
🧠 Use this if the PLC is non-responsive to software or hardware resets.
🔑 Method 4: Key Switch Reset (For Keyed PLC Models)
Fast and effective method for resetting using the onboard key switch.
Applies to:
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ControlLogix
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Some CompactLogix models
Steps:
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Turn the key to PROG (Program) mode.
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Wait a few seconds for the controller to halt the program.
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Turn the key to RUN mode.
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Observe if the fault clears.
🛠️ Perfect for field resets when software access isn’t available.
🧩 3. Additional Troubleshooting Tips
If a reset doesn’t resolve the issue, try these diagnostics:
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✅ Check fault codes: Use software or onboard LEDs to identify specific errors.
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🔌 Inspect I/O modules: Loose or malfunctioning I/O connections can trigger faults.
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🧰 Update firmware: Using outdated controller firmware can cause reliability issues.
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🔋 Check battery status: Some MicroLogix or SLC models require a working battery for memory retention.
📚 Rockwell Support Resources
📝 Final Thoughts
Resetting an Allen-Bradley PLC doesn’t have to be complicated—just be sure to:
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📦 Back up your program before doing memory resets.
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🛑 Understand the fault cause before clearing it.
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🧭 Use the correct method based on your PLC model and fault type.
Mastering these reset techniques empowers you to troubleshoot efficiently and minimize downtime across your automation systems.