Automation and controls troubleshooting is the process of identifying and resolving faults in industrial control systems, including PLCs, HMIs, sensors, actuators, relays, and communication networks. Effective troubleshooting minimizes downtime, reduces waste, and ensures safe, efficient operation.

Step-by-Step Troubleshooting Process

Understand the System

  • Review:
    • Electrical schematics
    • PLC ladder logic or code
    • I/O lists
    • Network layout
  • Understand the normal operation vs. current symptoms.

2. Identify the Symptoms

  • Is a machine not starting? Stuck in a cycle? Producing defects?
  • Are alarms or faults displayed on the HMI?
  • Use:
    • Operator feedback
    • Alarm logs
    • Status indicators (LEDs on PLCs, I/O modules, drives)

3. Check Power & Signals

  • Verify control voltages (e.g., 24VDC, 120VAC)
  • Check for blown fuses or tripped breakers
  • Inspect indicator LEDs for:
    • PLC CPU status (run, fault, stop)
    • I/O module indicators (input/output states)
    • Drives/VFDs (error codes)
  • Use a multimeter to test sensor power, relay outputs, etc.

4. Verify Inputs & Outputs

  • Check physical input device status (e.g., sensors, switches)
    • Use PLC diagnostic screen or programming software to confirm signal
  • Manually actuate inputs (e.g., press a limit switch)
  • Check outputs (e.g., relays, solenoids, motors)
    • Are they energized when commanded?
    • Use force/test functions in PLC software (with caution)

5. Check Communication & Networks

  • Inspect:
    • Ethernet/IP, Modbus TCP, or Profibus connections
    • Link/activity LEDs on switches or PLC ports
  • Look for:
    • Node or device communication errors
    • Incorrect IP addresses or duplicate nodes
  • Use tools like Wireshark, RSLogix, or TIA Portal diagnostics

6. Review PLC Logic

  • Trace logic from HMI input or sensor to final output
  • Check:
    • Setpoints and timer values
    • Logic conditions not being met
    • Fault latches or permissives (e.g., safety gates, E-stop)

7. Inspect Safety Circuits

  • Confirm:
    • Safety relays are reset
    • Emergency stops are disengaged
    • Door interlocks and light curtains are clear
  • Monitor safety inputs in PLC or safety controller

8. Test & Simulate

  • Use PLC/HMI test modes to simulate:
    • Sensor states
    • Motor commands
    • Alarms and resets
    • ** Always ensure test conditions are safe for equipment and personnel.

9. Document the Fault

  • Record:
    • Symptoms
    • Root cause
    • Steps taken to resolve
    • Preventive actions (if needed)