Hey there! I've been in that exact situation - midnight call, cryptic PLC errors, and a plant manager watching the clock tick away thousands of dollars. Here's my battle-tested emergency protocol:

1. First, take a deep breath and stay calm. Panic makes everything worse. Immediately notify your supervisor and the plant manager that you're on it - this buys you some breathing room.

2. Safety first! Ensure the area is secure and no one's in danger. Lock out/tag out if needed.

3. Document the exact error codes displayed on the HMI or PLC. Take photos if possible - this is crucial for troubleshooting and future reference.

4. Check the basics: power supply, connections, and any obvious physical damage. Sometimes it's as simple as a loose cable or tripped breaker.

5. Access your PLC documentation or error code manual. If you don't have it handy, use your phone to search the specific error codes online.

6. Connect your laptop to the PLC and check the diagnostic logs. Look for patterns - was there a sequence of events before the crash?

7. Try a controlled restart: power cycle the PLC (following proper shutdown procedures first). Many PLC errors clear with a simple reboot.

8. If the error persists, check I/O modules and field devices. Use a multimeter to verify signals are reaching the PLC correctly.

9. Keep the plant manager updated every 5-10 minutes. Even if you're not making progress, communication reduces their anxiety.

10. Have a backup plan ready - can you bypass the faulty section temporarily? Is there redundant equipment that can take over?

11. Once resolved, document EVERYTHING thoroughly. What failed, how you fixed it, and recommendations to prevent recurrence.

Remember: methodical troubleshooting beats frantic guessing every time. The pressure is real, but staying systematic is what gets production lines back up fastest!