Top Siemens SINUMERIK Error Codes Explained & How To Fix

Siemens SINUMERIK controls (especially 840D and 828D) report problems through multiple layers at once: the CNC (NCK) alarm, the drive system alarm (often SINAMICS S120), and the PLC message chain (machine builder logic). If you troubleshoot SINUMERIK effectively, you read the alarm as a stack, not a single line on the screen.

Alarm 2000 - PLC SIGN-OF-LIFE MONITORING

What it means
The CNC did not receive the expected cyclic “sign of life” from the PLC within the configured time window. The control typically goes NC not ready.

Common causes

• PLC stopped (service switch, programming stop, fault stop)
• PLC program stuck in a loop or overload
• PLC cycle time too slow for the monitoring setting

How to fix

• Check PLC state first: RUN/STOP and diagnostics
• Inspect PLC cycle time and any recent ladder changes
• If this started after a software update, verify PLC download and hardware configuration

Alarm 2001 - PLC HAS NOT STARTED UP

What it means
After power on, the PLC did not produce the first sign of life within the defined startup timeout.

Common causes

• PLC fails during startup sequence
• PLC download mismatch or missing OB calls
• Hardware module not initialized

How to fix

• Confirm the PLC boots cleanly and enters RUN
• Verify that the base program and required OBs are called
• Check recent hardware changes and module diagnostics

Alarm 2130 - 5V/24V ENCODER OR 15V D/A CONVERTER UNDERVOLTAGE

What it means
A power supply problem was detected in the encoder supply or the D/A converter supply. This is not subtle: it will break feedback stability and usually forces re-referencing.

Common causes

• Short circuit in encoder or cable
• Damaged encoder cable or crushed shielding
• Power supply rail instability inside the cabinet

How to fix

• Isolate the axis: disconnect the encoder cable and see if the alarm clears
• Inspect encoder cable routing, shielding, and connectors for oil ingress and pin damage
• Check the cabinet power supply rails under load

Alarm 3000 - EMERGENCY STOP

What it means
The emergency stop request is active via the NCK/PLC interface. The CNC is blocked until the safety chain is restored and acknowledged.

Common causes

• E-stop button pressed
• Door or guard circuit open
• Safety relay fault or broken wiring

How to fix

• Restore the safety chain and confirm door switches
• Check safety relay status and the E-stop acknowledgment logic
• Use PLC diagnostics to identify which safety input is open

Alarm 4000 - MACHINE DATA HAS GAP IN AXIS ASSIGNMENT

What it means
Axis-to-channel assignment in the configuration is not contiguous. This is a configuration integrity problem, not a machining problem.

Common causes

• Incorrect machine data after restore
• Mixed configuration from different machine variants
• Partial parameter load

How to fix

• Recheck axis assignment tables and channel mapping
• Reload a known-good machine data backup
• If you do not own the configuration, stop guessing and involve OEM or service

Alarm 4001 - AXIS DEFINED FOR MORE THAN ONE CHANNEL

What it means
A machine axis is assigned to multiple channels without a valid master channel definition.

Common causes

• Incorrect channel configuration
• Parameter restore from a multi-channel machine into a single-channel setup

How to fix

• Validate channel-to-axis mapping against the machine builder configuration
• Correct master channel settings where multi-assignment is intentional

Alarm 25000 - AXIS HARDWARE FAULT OF ACTIVE ENCODER

What it means
The control reports a hardware fault on the active encoder system for the axis.

Common causes

• Encoder hardware failure
• Cable or connector intermittency
• Encoder power or DRIVE-CLiQ chain instability

How to fix

• Reseat encoder connectors and inspect pins closely
• Check cable shielding continuity and cabinet grounding
• If the machine uses DRIVE-CLiQ, inspect the chain order and LEDs, then reseat modules

Alarm 25001 - AXIS HARDWARE FAULT OF PASSIVE ENCODER

What it means
Fault detected in the passive encoder channel.

Common causes

• Secondary encoder failure
• Wrong encoder parameterization

How to fix

• Confirm encoder type and parameterization match installed hardware
• Inspect the passive encoder wiring separately from the motor encoder

Alarm 25010 / 25011 - POLLUTION OF MEASURING SYSTEM

What it means
Measuring system quality is degraded. On machines with linear scales, this commonly shows up after contamination or damage.

Common causes

• Dirty or damaged linear scale
• Contaminated read head
• Coolant ingress into scale area

How to fix

• Inspect scale covers and wipers
• Clean the scale area carefully using approved methods
• Fix coolant splash paths and broken way covers to prevent repeat failures

SINAMICS S120 DRIVE FAULTS YOU WILL SEE WITH SINUMERIK

On 840D/828D machines with SINAMICS S120, drive faults often show as F-codes. Treat them as power, temperature, or electrical integrity problems first.

Fault F30003 - DC LINK UNDERVOLTAGE

What it means
The DC bus voltage is too low.

Common causes

• Incoming power dip or phase loss
• Weak supply transformer or loose terminals
• Regen resistor or power module issues that drag the bus down

How to fix

• Measure incoming line voltage while the fault occurs
• Check cabinet terminals, contactors, and fuses for heat marks and looseness
• Verify that auxiliary supplies and contactor logic are stable during spindle start

Fault F30004 - INVERTER OVERTEMPERATURE

What it means
The power unit temperature exceeded limits.

Common causes

• Clogged filters, failed fans
• Hot cabinet or poor airflow
• Overloaded axis due to mechanical resistance

How to fix

• Clean filters and confirm fan RPM and airflow direction
• Check cabinet temperature, not just the drive heat sink
• Reduce load and investigate axis binding or spindle overload

Fault F30005 - POWER UNIT I2T OVERLOAD

What it means
The drive has been overloaded for too long (current over time). This is often a symptom, not the root cause.

Common causes

• Mechanical overload or sticking axis
• Incorrect drive sizing or wrong motor data
• Aggressive acceleration and deceleration

How to fix

• Compare motor current and load during the move that triggers the fault
• Check mechanics: lubrication delivery, ballscrew condition, axis alignment
• Review ramp settings and confirm motor data matches the installed motor

Fault F07011 - MOTOR OVERTEMPERATURE

What it means
Motor temperature sensor reports overheating.

Common causes

• Overload
• Cooling failure
• Temperature sensor or wiring fault

How to fix

• Let the motor cool and retest under light load
• Check coolant or fan systems and motor ventilation paths
• Inspect sensor wiring and connector integrity

Fault F30021 - GROUND FAULT

What it means
Leakage to ground detected.

Common causes

• Damaged motor cable insulation
• Coolant ingress into connectors
• Motor insulation breakdown

How to fix

• Inspect motor cables for abrasion and oil damage
• Check connectors for coolant and contamination
• Perform insulation testing with proper procedures

PLC USER ALARMS 700.xxx (OEM MESSAGES)

Alarms in the 700.xxx range are typically generated by the machine builder PLC logic. The number alone is not enough: the text and the PLC signal driving it matter more than the code. For persistent 700.xxx alarms, go straight to the PLC diagnostics screen, trace the input condition that raised it, and verify the missing readiness signal.

Practical notes for SINUMERIK troubleshooting

Treat SINUMERIK alarms as a chain of evidence. If the machine says “NC not ready,” determine whether the PLC is alive, whether safety is blocking, whether configuration integrity is broken, or whether axis feedback is unreliable. Then confirm the drive layer state with SINAMICS diagnostics. Repeatable alarms at the same motion point usually indicate mechanics, feedback, or power quality issues rather than random software behavior.

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