What causes fault code AB-F001 (PLC Major Recoverable Fault)?

Watchdog timer expired — program execution exceeded time limit. Stack overflow — excessive subroutine nesting or recursion. Invalid memory access — array index out of bounds. Math overflow — result too large for data type. Motion group fault — servo drive reported error to processor

How do I fix fault code AB-F001?

Check fault code in Controller Properties > Major Faults tab in Studio 5000. Fault Type 4 Code 16 = watchdog: increase task watchdog time or optimize program. Fault Type 4 Code 20 = stack overflow: check for recursive JSR calls. Fault Type 4 Code 34 = motion fault: check axis faults in motion group. Clear fault and switch from Faulted to Run mode. If fault recurs immediately, the root cause is still present

PLC Major Recoverable Fault

AB-F001

ControlLogix/CompactLogix processor encountered a major fault that can be cleared without reprogramming.

high allen-bradley

allen-bradley plc major fault controllogix compactlogix

Probable Causes (ranked)

Watchdog timer expired — program execution exceeded time limit
Stack overflow — excessive subroutine nesting or recursion
Invalid memory access — array index out of bounds
Math overflow — result too large for data type
Motion group fault — servo drive reported error to processor

Fix Steps

1 Check fault code in Controller Properties > Major Faults tab in Studio 5000
2 Fault Type 4 Code 16 = watchdog: increase task watchdog time or optimize program
3 Fault Type 4 Code 20 = stack overflow: check for recursive JSR calls
4 Fault Type 4 Code 34 = motion fault: check axis faults in motion group
5 Clear fault and switch from Faulted to Run mode
6 If fault recurs immediately, the root cause is still present

Field Trick

Go online with Studio 5000, right-click the controller icon, select Properties, then Major Faults tab. It tells you EXACTLY which instruction and routine caused the fault.

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