PLC I/O Loop Failure
HARDWARE PATH
SOFTWARE PATH
Terminal Loose?
NO
YES
Tighten Terminal Screws
Check I/O Module & Channel LEDs
Red/Blink Fault LED?
NO
YES
Replace Faulty Module Card
Measure Voltage at Terminals
Voltage Invalid?
NO
YES
Fix Field Power / Sensor Wiring
PLC Software Online?
YES
NO
Restore Software Link & Drivers
I/O Bit Forced?
NO
YES
Remove Force & Update Logic
Network Errors?
NO
YES
Resolve Fieldbus / IP Conflict
Scan Cycle Overrun?
NO
YES
Optimize Watchdog Timer
Field Device / Wiring Fault Verified
PLC Controller / Memory Fault Verified