Sequence Step Not Advancing

Walt — Simple Man Takeaway

The step is not stuck because it hates you. It is waiting for a truth the machine never received.

Plain-English Summary

Use this flow when a sequence, index, state machine, station, or cycle stage remains active and the expected next step never becomes active.

R.E.A.L. firstRead-only firstCapture before changingReverse-trace failed conditionsTrap intermittent ghosts

First-Check Flow

1. Identify the current active step

Find the step bit, state number, sequence index, or active stage that is stuck.

2. Identify the next expected step

Determine exactly which step should come next and which transition rung controls that move.

3. Find the transition condition

Open the transition rung/logic and identify the conditions required to leave the current step.

4. Reverse-trace the blocking condition

Ignore true conditions. Pick the false condition stopping transition and trace backward to its driving OTE/result.

5. Check motion complete and feedback

Confirm actuator complete, sensor made, timer done, drive ready, robot complete, and downstream ready as applicable.

6. Use Ghost Busting™ for late, skipped, or self-clearing steps

If the sequence only sticks sometimes or clears before you are online, select the suspect cycle stage on the HMI and trap it.

Field Checks

Current active step identified
Next expected step identified
Transition rung / transition condition located
False blocking condition found
Motion-complete feedback checked
Timer/counter/permissive/interlock checked
Handshake with downstream/upstream equipment checked

Watch Out For

Looking at the wrong step chain or recipe path
Chasing all transition contacts instead of the failed one
Missing a reset/unlatch that immediately clears the next step
Sensor made too late or not long enough
Robot/drive/cell handshake completed but wrong bit consumed
Intermittent transition that occurs between scans or before a person sees it

Reverse-Trace or Ghost Busting™?

Use Reverse-Trace Logic Solving™
when the failure is stable and visible live. Open the PLC program, monitor in RUN mode, chase only failed conditions, find the driving OTE, and repeat failure-to-failure.

Use Ghost Busting™
when the failure is intermittent, self-clearing, timing-based, or disappears before maintenance sees it. Select the suspect routine from the HMI and let the comparator trap expected-vs-actual mismatch every scan.

Find the failed result. Identify the blocking condition. Reverse-trace only what is failing. If the truth disappears, trap the ghost.

Related Calculators / SWAT Screens

Industrial Controller™ PLC / PAC I/O Spare Capacity Sensory King™ Sensor False-Trigger Clue Screen

Walt says STOP! - Safety First

Make these checks prior to proceeding.

Do not bypass safety, force outputs, defeat guards, or work live beyond your qualification and site procedure. If motion, stored energy, live electrical exposure, lockout/tagout requirements, or personnel inside guarded areas are involved, stop and follow the required safety process.