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The thermal sensor in an axis motor has gone over its limit. The motor has spent a while delivering more current than it can shed as heat. As with overloads, the alarm arrives after a long period of effort: by the time it trips, the problem has been there for some time.
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 it returns after cooling down or with no load.
Reset once cooling is confirmed and the cause is removed.
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 servo motor winding carries a thermal sensor that opens or changes resistance when a temperature is exceeded, and that signal reaches the amplifier. It is a direct measurement, different from the calculated thermal model that trips overload alarms: here the heat is not estimated, it is measured. That makes this alarm fairly conclusive: if it trips, either the motor really is hot or the measuring chain is broken. A servo motor heats up by three routes. The first is sustained current: the axis is pushing against abnormal mechanical resistance, or the cutting process demands a continuous force beyond what is reasonable. The second is duty cycle: very frequent accelerations and decelerations generate repeated current peaks, and in programs with thousands of short moves, typical of surface finishing, the motor can heat up without any single cut looking heavy. The third is heat evacuation: a motor covered in chips and oil, with its fins blocked or installed in a corner with no air circulation, cannot even shed its normal heat. And there is a particular case with vertical axes: there the motor holds the weight even at standstill if the brake is not helping, so it can heat up without moving, which is a symptom that confuses everybody the first time.
In order, from the fastest and cheapest check to the most expensive.
01Stop and let it cool before trying anything else
A hot motor that keeps being pushed gets genuinely damaged: the winding insulation degrades cumulatively. Stop producing on that axis and let the temperature come down before any test. Do not simply drop the feed rate to keep going.
02Check whether the motor really is hot
With the machine stopped and working safely, judge the temperature of the motor casing. If it is clearly hot, the cause is thermal. If it is cold and it still alarms, suspicion falls on the sensor, the cable or the connector, and that is maintenance.
03Check the motor can shed heat
Fins and casing caked with chips and oil, motor fan stopped if it has one, motor wedged where no air circulates. Cleaning a motor covered in chips and coolant is one of the most profitable interventions there is, and it is done with the machine stopped.
04Check the axis's mechanical resistance
Lubrication, ways, bellows, stiffness when jogging, compared against another axis. Everything that makes an axis stiff ends up in the motor as current and heat. If the axis is stiff, this alarm is a consequence and not the cause.
05Look at the kind of program that was running
Finishing passes with millions of short segments, with continuous acceleration and deceleration, heat things up far more than a steady roughing cut. If the alarm always appears on that kind of job and never in roughing, the problem is the duty cycle and it is fixed by smoothing the path or the CAM tolerances.
06If it is a vertical axis, suspect the brake
A brake that does not hold forces the motor to carry the weight continuously, even during waits. The symptom is a motor heating up with nothing in the program to justify it. Maintenance checks it, and it is a safety matter as well.
Duty cycle: continuous acceleration and deceleration. It is confirmed by the kind of program. Fix it by smoothing the path in CAM, reviewing the segmentation tolerances and adjusting accelerations if the builder allows it.
Heat evacuation blocked. It is confirmed because the alarm appears sooner than on other axes with similar load. Fix it by cleaning and protecting it, and by checking where coolant is reaching it from.
The measuring chain: open thermal sensor, cable or connector. It is confirmed by the contradiction between touch and alarm. It is an electrical maintenance diagnosis; a thermal sensor is never defeated or bypassed to keep working.
Cleaning of motors and the axis area inside periodic maintenance, especially where chips and coolant fall. Proper lubrication, which is what keeps the required current low. Bellows and guards intact. Smoothed finishing paths, with sensible segmentation tolerances, so the axes are not punished with pointless accelerations. Vertical axis brakes checked. And note when it trips: if it is always on the same kind of job, the answer is in the programming and not in the machine.
Fanuc detects overtemperature in the servo motor of an axis through the thermal sensor. It is an alarm from the Power supply area, and in the catalog it is listed as “Servo motor overtemperature”. On the machine you notice it like this: Axis overheated, Alarm after long movements or heavy loads, May come up when braking repeatedly.
On the shop floor it almost always comes from one of these causes: Mechanical overload, Poor lubrication, Insufficient ventilation, Excessive accelerations, Thermistor cable. Rule out the most likely one on your machine first, before touching parameters or swapping anything.
Reset once cooling is confirmed and the cause is removed. Resetting without fixing the cause first only hides the problem: OH0702 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: Let it cool down, Check the axis load, Check lubrication and guides, Reduce empty test speeds. That alone will tell you whether it is the program or whether you need to raise a maintenance job.
With OH0702 active, avoid this: Do not keep producing with a hot motor, Do not bypass the thermal sensor, Do not machine at reduced feeds without diagnosing the cause. Skipping any of these points is what turns a minor stop into an expensive breakdown.
If it returns after cooling down or with no load. 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.
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