Fanuc PSM Alarm 2 (Internal Cooling Fan Stopped) — Causes, Diagnosis & Fixes

Alarm 2JJ Automation

Alarm 02 on a Fanuc αi Power Supply Module (PSM) means the module's internal cooling fan has stopped. The PSM shows 02 on its 7-segment display and the whole drive system drops — because the PSM feeds the DC link for every servo and spindle amplifier on the machine, a PSM protection alarm takes everything down with it. The fault itself is usually a ₹-few-thousand fan; the risk of ignoring the pattern is a heat-killed PSM that takes the machine down for days. This is the PSM sibling of SVM alarm F, and the diagnosis is nearly identical.

Step 1 — Confirm and inspect (10 minutes)

  1. Locate the internal fan — on most PSM αi units a slide-in fan cassette at the top of the module (the external heatsink fan at the cabinet rear has its own separate alarm/overheat path).
  2. Power up safely and observe: not spinning, twitching, or spinning slowly = confirmed. A fan that runs after a nudge (power OFF before touching) has worn bearings — replace it; it will strand you again within weeks.
  3. Dust first: the classic find is a fan stalled solid by oil-laden dust. Blow out the fan and module vents (power off). If it spins up and the alarm clears, still schedule a fan replacement — a stalled fan has cooked its windings.
  4. Reseat the fan connector — brittle crimps and vibration-loosened plugs are regular culprits.
Tip: The PSM's fan sits highest in the cabinet's warm-air column on many layouts — it runs hotter and dies first. When it goes, check every SVM/SPM fan in the row the same day; they breathe the same dust and are the same age. Fans are 3–5-year consumables in a dusty shop — replace as a planned set, not as serial breakdowns.

Step 2 — Replace the fan unit

  1. Use the correct Fanuc fan cassette for your PSM model (spec on the nameplate/parts list). Match the airflow arrow on installation.
  2. Generic two-wire fans will not work: the PSM monitors fan rotation through a sense signal — a fan without the sense wire reads as ‘stopped’ even at full speed and the alarm stays on. This is the single most common reason a ‘new fan’ does not fix alarm 02.
  3. Power up, confirm 02 clears and the fan runs at full speed.

Step 3 — If a genuine fan does not clear it

  • Fan power / sense circuit fault on the PSM control board — the fan is healthy but its supply or the rotation-sense input has failed. Board-level repair; we see this on units where the old fan stalled and dragged the drive transistor down with it.
  • Wrong fan variant — same frame, different connector/pinout across PSM generations; verify against the module's parts list.
  • Alarm history check: if 02 alternates with overheat or DC-link alarms, the module has been running hot for a while — have the capacitor bank checked before it becomes an undervoltage or rectifier failure.

While the cabinet is open

A stopped PSM fan is frequently the first symptom of a cabinet-cooling problem: clogged door filters, a failed heat exchanger or cabinet AC, or summer ambient pushing everything over the edge. Clean the filters, verify the exchanger, and feel the PSM heatsink after a heavy cycle — if you cannot hold it for 5 seconds, cooling is marginal even with the new fan. Heat is what actually kills PSMs: dried bus capacitors and stressed rectifier/IGBT stages.

Related guides

PSM alarm 2 that a new fan didn't fix — or a PSM already heat-damaged? JJ Automation stocks genuine-spec Fanuc fan units and repairs PSM modules at component level — fan-drive circuits, capacitor banks, rectifiers — with real load testing before dispatch. Tested exchange PSMs in stock, on-site diagnosis in NCR. WhatsApp us or call +91 88022 12394.
Tags: Alarm 2, Cooling fan, Fanuc, Power supply module, Psm, Troubleshooting