Siemens Sinumerik Alarm Codes: Categories, Common Alarms, and Troubleshooting

Key takeaways

• Sinumerik alarms are organized by number range: NCK core alarms, 25xxx measuring-system (encoder) alarms, 300xxx drive and axis alarms, 4xxxx channel and mode-group alarms, and 700000+ PLC or machine-builder alarms.
• The alarm text and parameters (axis name, drive number, error value) usually identify the failing component more precisely than the number alone.
• 300xxx drive alarms point at the drive system: enable signals, DC bus, motor cables, or the motor itself. 25xxx alarms point at encoders, cables and shielding.
• Alarms in the 700000+ range come from the machine builder's PLC program, so their meaning is specific to your machine, not to Siemens documentation.
• Exact meanings vary between 810D, 840D sl and Sinumerik ONE. Always confirm the code in the Diagnostics Manual for your control generation before replacing parts.

When a Sinumerik control stops with an alarm, the number range tells you which subsystem raised it and the alarm text tells you where to look. This guide is for maintenance technicians and plant engineers who need to classify a Sinumerik alarm fast, run sensible first checks, and reset it safely on 810D, 840D and Sinumerik ONE machines.

How Sinumerik alarms are organized

Siemens groups alarms by source subsystem, and the number range is the key. Reading the range first saves you from chasing the wrong cabinet.

One structural point that confuses new technicians: two documents describe your machine. Siemens documents the NCK, drive and encoder alarms. The machine builder documents everything in the 700000+ range, because those alarms come from the builder's own PLC program. If the alarm text mentions a guard, a magazine, a lubrication unit or a conveyor, it is almost always a builder alarm.

Reading an alarm properly before touching anything

A Sinumerik alarm line carries more than the number. Note all of it before resetting, because the alarm text disappears with the reset and the parameters are the diagnostic gold.

• The axis or spindle name in the text (X1, Z1, SP) tells you which drive or encoder raised the fault.
• The fine detail or error value shown with many drive alarms narrows the cause, for example distinguishing an enable-signal problem from a measured overcurrent.
• The alarm history in the diagnostics screen shows the order in which alarms arrived. The first alarm is usually the cause, the rest are consequences.

Write the full line down or photograph the screen, then check the history. A drive alarm that always follows an encoder alarm is a symptom, not the disease.

300xxx drive alarms: the enable chain and the hardware

The 300xxx range covers the drive system: infeed, drive modules, motor cables and motors. In practice the most frequent culprits are not burned electronics but the enable chain: emergency stop circuits, guard door switches, drive enable terminals and contactors that feed the infeed module. If several axes drop out at once, suspect the common enables and the infeed before any individual drive.

Sensible first checks, in order:

1. Check whether the emergency stop circuit is healthy and all guard doors report closed.
2. Look at the infeed module LEDs and DC bus status. No bus voltage means no axis will enable, regardless of what the individual drives say.
3. Inspect motor power and feedback connectors on the affected axis for coolant ingress and loose locking rings, a very common root cause on machines with flood coolant.
4. Only then consider the drive module or motor. A qualified electrician can insulation-test the motor and cable after lockout.

Safety note: drive cabinets store energy in the DC bus capacitors well after power off. Lock out, wait the discharge time stated on the module, and verify with a meter before touching power terminals. Never bridge door switches or enable signals to test, and support vertical axes mechanically before releasing any brake. The same discipline applies on other controls; the Fanuc equivalent readiness fault is covered in our Fanuc alarm 401 (VRDY OFF) guide.

25xxx encoder and measuring-system alarms

Alarms in the 25000 range mean the control does not trust the position feedback. Typical texts mention encoder hardware, signal amplitude or zero-mark monitoring. The physical causes are mundane and mechanical far more often than electronic:

• Contaminated or damaged feedback cables, especially where they flex in cable tracks.
• Coolant in connectors, which degrades signal amplitude intermittently, so the alarm comes and goes with vibration and temperature.
• Damaged shielding or poor grounding, which lets drive noise corrupt the encoder signals under load.
• A genuinely failing encoder, often after a crash or years of thermal cycling.

Distinguishing a bad encoder from a bad cable or drive input is a swap-and-observe exercise. Our guide on encoder failure symptoms and testing walks through the checks in detail, and they map one-to-one onto Sinumerik 25xxx alarms.

Common NCK alarms worth knowing

Two examples show how the NCK range behaves. Alarm 10910 and its neighbours report contour and velocity violations: the programmed path demands more than the axis dynamics allow. The fix lives in the program or the tool data, not in the cabinet. Program-syntax stops similarly point at the part program: a corrupt transfer, a missing tool offset, or an edit made at the machine.

The practical rule: if the alarm range is below 10000 and the machine ran fine yesterday, ask what changed in the program or offsets before opening any door. Interview the operator, check the last edits, and compare against a known-good version of the program.

PLC and machine-builder alarms (700000+)

These alarms are written by whoever built the machine around the Siemens control. Lubrication pressure, chip conveyor overload, tool magazine position, guard locks and coolant level all report here. The Siemens Diagnostics Manual cannot help you; the machine builder's electrical drawings and alarm list can.

If the builder documentation is missing, the underlying logic often reads like the faults covered in our Siemens S7 PLC SF fault LED troubleshooting guide: an input that never arrived, a sensor that failed, or a timer that expired waiting for a confirmation switch. Trace the alarm number to the PLC message text, then to the sensor or actuator it monitors.

Resetting safely: cancel, reset, and power cycle

Sinumerik distinguishes alarm classes by how they clear. Some clear with the Cancel/Alarm Cancel key, some need Reset on the machine control panel, and drive faults frequently require a full control power cycle before the drive re-enables. The alarm help text states the clearing condition.

Two rules keep resets from making things worse. First, fix or at least understand the cause before resetting; repeatedly resetting into an overcurrent can destroy a marginal drive module. Second, after any encoder or drive work on an absolute-referenced axis, verify the reference position against a physical datum before running a program. An axis that lost its bearings will happily execute a perfect crash.

Track alarms as downtime, not as folklore

A Sinumerik machine that throws the same 25xxx alarm every few weeks has a failing cable or connector, and the only way that gets an engineering fix instead of a shrug is a record. Log every alarm stop as a downtime event with the alarm number as the cause code, and track MTBF per machine and per alarm family. Chronic offenders then surface in the data with their real cost attached, which is what justifies replacing a cable track or an encoder on schedule instead of at 2 a.m.

That fault history also makes the repair itself faster: the technician who sees that the last three stops on this axis were all signal-amplitude alarms goes straight to the connector with contact cleaner and a crimp kit. This measurement-first habit is the core of OEE for manufacturing: availability losses only shrink when they are counted honestly.

Where Fabrico fits

Manual downtime logs miss short stops, and operators rarely type alarm numbers into a spreadsheet at the end of a shift. Fabrico is computer-vision-verified OEE plus closed-loop maintenance execution: cameras catch stops and micro-stops that manual logs and sensors miss, and maintenance work orders close the loop from detection to fix, so every Sinumerik alarm stop becomes a counted, categorized event with a work order trail. If your alarm history lives in operators' memories today, book a Fabrico demo and see what verified downtime data changes.

Because Sinumerik machines run Sinamics drives underneath, the drive-side fault families are covered in our Sinamics drive fault codes guide.

Frequently asked questions

What do Sinumerik 300xxx alarms mean?

They come from the drive system: infeed, drive modules, motor cables, motors and their enable signals. Check emergency stops, guard doors, DC bus status and motor connectors first, then the specific drive and motor. The exact fine code is documented in the Diagnostics Manual for your control generation.

What causes Sinumerik 25xxx encoder alarms?

Damaged or contaminated feedback cables, coolant in connectors, degraded shielding, or a failing encoder. Intermittent alarms that appear under load or vibration usually point at cables and connectors rather than the encoder itself.

Why can I not find my alarm number in the Siemens manual?

Alarms numbered 700000 and above are created by the machine builder's PLC program, not by Siemens. Their meanings are specific to your machine and are documented in the machine builder's alarm list and electrical drawings.

How do I reset a Sinumerik alarm?

Depends on the alarm class: some clear with the Cancel key, some with Reset on the machine control panel, and many drive alarms only clear with a full power cycle. The alarm help text names the clearing condition. Always address the cause first, and verify axis reference positions after encoder or drive work.

Are Sinumerik alarm codes the same on 810D, 840D and Sinumerik ONE?

The range structure is similar but exact numbers, fine codes and texts differ between generations and drive families. Confirm the meaning in the Diagnostics Manual matching your control and drive system before replacing hardware.