We use technical and security cookies and, only if you accept, analytics with no cross-site tracking. More in the Cookie policy and Privacy policy.
We use first-party cookies and technical storage to make the site work, Google reCAPTCHA security technology and, only if you accept, Vercel analytics (no cookies, no cross-site tracking). You can accept or reject analytics; both options are equivalent and you can change your choice at any time. More info: Cookie policy, Privacy policy, Legal notice and Terms and conditions.
A fan has stopped, or an area of the control or the cabinet has gone over the permitted temperature. It is a cheap alarm to fix and a very expensive one to ignore: sustained heat is what ages capacitors, power supplies and modules, and it is behind a large share of the electronic failures that later show up as mysterious faults.
For reference only: alarms change with the manufacturer, the control and the machine PLC. Check the full code in the official manual before doing anything. Legal notice.
If the fan does not turn or the temperature does not drop.
Reset after cooling and recovering ventilation.
Choose the manual matching your control series, software version and machine builder. A support portal is a starting point; it does not establish applicability to every model.
The electrical cabinet and the control units are cooled by forced air: fans draw filtered air, push it through the heatsinks and expel it. There are temperature sensors at the critical points and, on many fans, a rotation signal that lets the system know whether they are actually turning. The supervision trips if a fan stops turning or if the temperature at a point goes over the threshold. The mechanism is cumulative, which is why the moment it appears carries a lot of information: if a filter clogs gradually, airflow drops gradually, the internal temperature climbs a few degrees each week, and one day the hottest point crosses the threshold in the afternoon, when the shop is at its warmest. The machine had been warning you silently for months. The other typical cause is a fan whose bearings are seizing: first it makes noise, then it turns more slowly, then it stops. And there is a variant that misleads people: cooling that works but with the airflow disturbed because somebody left a cabinet door open to cool things down, which actually breaks the designed air circuit and lets dust in, or because material was stacked against the outlet grilles.
In order, from the fastest and cheapest check to the most expensive.
01Note what time it appears and how long the machine has been on
If it always comes up after a certain time of day or after several hours of running, it is thermal accumulation: filters, ambient or airflow. If it comes up shortly after switching on, a stopped fan or a sensor is more likely. This costs nothing to check and steers everything else.
02Check what is accessible from outside
Inlet and outlet grilles clear, with no material stacked in front and no bags or rags. Cabinet filters in plain sight: if they are grey and matted, you already have a cause. Cleaning or replacing filters is done with the machine stopped.
03Listen to the fans
With the machine switched on and from outside, listen for them turning and for any that sounds different from usual. A fan that squeals or hums irregularly is about to stop. If one clearly makes no sound, you know which one to check, but opening the cabinet to verify it is a maintenance job.
04Measure the shop ambient temperature next to the machine
Machines have a permitted ambient temperature range, and in summer many shops exceed it by mid-afternoon. If the ambient next to the machine is above what the manual states, no filter will fix it: the building has to be ventilated or the machine moved away from heat sources.
05Let it cool and see whether it repeats
Switching off and letting it cool clears the alarm, but that is not a diagnosis. What is useful is seeing whether it returns after the same running time. If it is reproducible by running time, the cause is cooling; if it comes straight back with the machine cold, suspect the sensor or the fan itself.
06Fan replacement and internal inspection go to maintenance
Changing a cabinet or control unit fan means working inside the cabinet with the machine locked out, and the correct model has to be fitted with the airflow direction respected. A fan mounted backwards cools worse than none at all. Never work with the cabinet open and energised, and never leave it open to cool things down.
Cooling at its limit from ambient temperature plus dirty filters. It is confirmed by the time-of-day pattern and by looking at the filters. Fix it by cleaning or changing filters and, if it still returns, by acting on the shop ventilation.
A stopped fan or a temperature sensor with a problem. It is confirmed by listening and, once inside the cabinet, by maintenance. If it is the sensor, the cabinet will be at normal temperature and still alarm.
The dust was redistributed inside instead of removed, or something was damaged. Blowing out a cabinet without extracting the dust drives it into the places where it does most harm. Correct cleaning is by vacuum with filters replaced, with the machine locked out.
Cabinet filters on the maintenance plan at a fixed interval, adjusted to how dirty the shop is, with spares in stock. Cabinet cleaning by vacuum, never by blowing. Fans replaced preventively as soon as they start making noise, without waiting for them to stop. Grilles always clear, with a marked area around the machine where nothing is stacked. Shop temperature controlled in summer. And the date of each cleaning recorded on the machine itself so anyone can see at a glance when the next one is due.
Fanuc/OEM detects fan stop or overheat condition. It is an alarm from the Power supply area, and in the catalog it is listed as “Fan or overtemperature”. On the machine you notice it like this: Alarm after machine on time, Cabinet or drive running hot, Fan stopped or noisy.
On the shop floor it almost always comes from one of these causes: Faulty fan, Clogged cabinet filter, High ambient temperature, Drive overloaded. Rule out the most likely one on your machine first, before touching parameters or swapping anything.
Reset after cooling and recovering ventilation. Resetting without fixing the cause first only hides the problem: OH0701 trips again and, in the meantime, you keep working with the machine in bad shape.
With the machine stopped and in a safe state, start with these checks: Check external ventilation, Clean filters with the machine stopped, Record temperature/time of appearance. That alone will tell you whether it is the program or whether you need to raise a maintenance job.
With OH0701 active, avoid this: Do not bypass safety devices, Do not manipulate energized electrical cabinet, Do not continue producing if the alarm reappears. Skipping any of these points is what turns a minor stop into an expensive breakdown.
If the fan does not turn or the temperature does not drop. If you are not sure how far it goes, stop the machine and report it: a repeat alarm always works out cheaper than a crash.
It is critical: there is a real risk of damage to the machine, the tool or a person. Leave the machine stopped, do not keep resetting it to see if it goes away, and call maintenance before producing again. Guidance reference. Always confirm the full text in the exact machine/control manual.
List of G and M Codes for CNC Programming. Search and filter ISO commands by control, machine or function.
CNC IDE: editing with G/M tooltips, line inspector, conversion between controls and 2D/3D toolpath.
Estimate CNC turning and milling cycle time from G-code. Calculate parts per hour with a breakdown of cutting, rapids, canned cycles and tool changes.
