ControlLogix Major Fault Type 4 Code 34 (Negative Timer)

Q: What causes Rockwell Automation / Allen-Bradley ControlLogix / CompactLogix (Logix 5000) fault T04:C34?

1. Preset written from a calculation that can go negative: Find every write to the timer .PRE and limit the result to zero or above. 2. Preset or accumulator written from an HMI, recipe or message: Check the source value and add a range check in the HMI and in the program.

A timer instruction had a negative value for its preset (.PRE) or accumulated value (.ACC). Rockwell’s corrective action is to fix the program so that it cannot load a negative value into the timer preset or accumulated value.

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Upload a keypad photo, the fault history or a parameter export from your Rockwell Automation / Allen-Bradley ControlLogix / CompactLogix (Logix 5000). InduQT compares the evidence and suggests the next useful checks.

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When it happens

When the timer instruction executes with the bad value

Likely causes and checks

1Preset written from a calculation that can go negative

Points to it: The .PRE is set by MOV/CPT from another value, e.g. a difference or scaled input.
Check: Find every write to the timer .PRE and limit the result to zero or above.

2Preset or accumulator written from an HMI, recipe or message

Points to it: Fault follows an operator entry or recipe download.
Check: Check the source value and add a range check in the HMI and in the program.

Telling it apart

The fault names the program and routine; the timer tag is in the faulted rung, but the bad value is usually written elsewhere, so cross-reference the .PRE and .ACC writes.

Evidence to collect

Major Faults tab screenshot
Timer tag values (.PRE, .ACC) at the fault
Cross-reference of writes to the timer tag
HMI or recipe entries just before the fault

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Rockwell Automation / Allen-Bradley ControlLogix / CompactLogix (Logix 5000) fault T04:C34: Program fault: timer with a negative PRE or ACC