FANUC Troubleshooting Guides, Repair Tools and Remote Support

Welcome to the CNCShare English section — practical, field-tested guides on FANUC CNC electrical commissioning, PMC ladder programming, servo tuning, alarm diagnosis and troubleshooting.

Everything here is written for engineers who are standing in front of a machine: what to look at first, which number to read, and what a given value actually means. No theory for its own sake.

Not sure where to start? Jump to the “Which guide do I need?” section at the bottom — it maps the most common field situations to the right article in four questions.

← Browse all English articles (full list)

1. PMC Ladder Programming and Project Workflow

Start here if you need to read, write, or deliver a PMC sequence program.

• FANUC PMC Ladder Diagram Beginner Tutorial — basic vs function instructions, the difference between sequential execution and relay logic, and two complete examples (tool magazine positioning + spindle coolant timer). Start with this if ladder is new to you.
• FANUC PMC Project From Scratch: The 6-Stage Flow — how to run a whole PMC project: site survey, full backup, address planning, safety-first logic, online download, staged verification. Includes the five things to hand over and the four steps people skip. This is the methodology backbone of the series.
• FANUC PMC: Edit on PC and Send Back to NC — getting the ladder onto a PC and back to the machine. Covers version matching, edit format vs memory card format, serial setup, and the critical READ = in / WRITE = out distinction.
• FANUC LADDER III: Compile, Decompile and Program Protection — why you must compile before downloading and decompile before editing, plus how password protection works and why a lost password cannot be recovered.
• FANUC PMC Troubleshooting: 5 Real Cases — spindle not starting, ATC timeout, E-stop that won’t reset, lube pump timer fault, hydraulic chuck no action. Uses a four-step signal-tracing method.
• FANUC PMC External Alarm Reverse Lookup — when the control shows an external/manufacturer alarm (1000–2999 range), how to go from the alarm number to its A address, trace the ladder, reach the I/O point, and confirm by forcing the signal. Includes the “signal present but no alarm” trap.
• FANUC Data Backup and Recovery: ALL I/O, BOOT SRAM and CF Card Sizing — the three backup routes, what actually lives in SRAM versus FROM (the ladder is in FROM, and it does not come back with an SRAM-only restore), and the CF capacity limits that matter.
• Fanuc Macro B Guide: Variable Partitions, G65/G66/G67 Calls — variable common vs local partitions, the G65/G66/G67 macro-call forms and nesting limits, with the PS alarms to watch.
• FANUC LADDER III — version selection for 0i-D/F/MF, installation without the classic failures, and the five beginner pitfalls with their fixes.

2. Diagnosis and Fault Finding

Start here when something is wrong but you are not sure what.

• FANUC Diagnosis Numbers (DGN) Quick Reference — 100+ diagnosis numbers grouped by function (000–039 execution, 200–299 servo, 300–399 position, 400–499 spindle, 500–605 overtravel and PMC), with alarm cross-reference and how to view/export them on your machine.
• FANUC No-Alarm Fault Diagnosis — the hardest class of fault: nothing on the screen, but the machine won’t move. Maps it to DGN000 (M-code not confirmed), DGN003 (in-position check) and DGN005 (axis interlock), with the interlock signal table.

3. Servo Tuning

Start here for vibration, overshoot, noise or contouring problems.

• FANUC Servo Gain 2021 / 1825 Adjustment — official starting values, the inertia-ratio conversion formula, the 5000 vs 50–80 unit confusion explained, semi-closed vs full-closed loop, and waveform-to-parameter interpretation.
• CNC Servo Vibration, Overshoot and Noise — classifies the four kinds of “shake” (high-frequency squeal, low-frequency flutter, start/stop overshoot, machining ripple) and gives the right branch for each. Also covers HRV filters and when to stop tuning and check the machine.
• FANUC Inertia Ratio: Hand Calculation, Parameter 2021 — get the load inertia ratio right before touching gain — the hand calculation, the conversion, and how the series differ.
• Fanuc Backlash Compensation 1851: Measure, Convert, Verify — measuring backlash, converting it into detector units, and checking the result instead of over-compensating.
• Fanuc Pitch Error Compensation 3620–3624: Laser Measurement to Verification — point numbering, parameter entry, and the accuracy check that has to follow.
• FANUC Servo Amplifier: Repair or Replace? — the four cost items — direct, downtime, risk and hidden — plus a decision table for swap versus repair.
• SINUMERIK Contour Error and Following Error Tuning — Kv factor, feedforward and friction compensation on 828D/840D, with the 25050/25040/25080 monitoring alarm order and a circularity test to prove the result.
• FANUC SERVO GUIDE — waveform capture at 48 kHz, FFT notch filtering, rigid tapping and HRV modes, with the backup-first safety discipline for servo tuning.

4. FANUC Alarm Code Reference (6 Parts, 0001–5559)

A complete working English reference for FANUC P/S (Program / Setting) alarm numbers, split by range so you can look up a code the moment it appears on screen. Each part lists the alarm message and the practical meaning or first action.

• Part 1 — P/S 0001–0224 — tape and format errors, G code and feed, circular interpolation, tool compensation, reference position return, program and sequence numbers, macros, rigid tapping.
• Part 2 — P/S 0230–0461 — canned and compound cycles, nano smoothing, synchronous / mixed / superimposed axis control, skip functions, tool life, real-time macros.
• Part 3 — P/S 0492–1308 — 3D interference check, Cs contour control, thread cutting, macro syntax and variables, program registration, G10 parameter input.
• Part 4 — P/S 1332–1973 — 3D handle feed, normal direction control, M code duplication, index table, program security, EGB, RS-232C, USB memory and memory card.
• Part 5 — P/S 2032–5110 — Ethernet and data server, P-CODE macros, peripheral axis control, sheet-metal and punch-press cycles, nibbling, program limits and feedrate.
• Part 6 — P/S 5130–5559 — PMC axis overlap, flexible synchronous control, tool management and interference, Cs contour control, tilted surface machining G68.2, option authentication.

5. System Alarms, Power, Other Brands & Machine Checks

Start here for board-level and power-related faults, and for non-FANUC controls.

• FANUC System Alarm 950 / 971 / 974: Meaning and Board-Level Diagnosis — these are system/PSM alarm numbers that point at a hardware or drive board, not a parameter. How to read the sub-code, isolate the suspect board, and what an external alarm (900–976) actually means.
• FANUC Battery Alarm 306 / 307: How to Replace Without Losing Zero Return — the absolute-position battery is low. The safe order to swap it, why you must keep the axis powered during the change, and how to recover the reference position if it is lost.
• FANUC MPG Handwheel Not Working? — when manual pulse generation doesn’t move the axis: signal-chain check from the handwheel encoder through the I/O to the parameter, and the common cause (HS21/HS22 selector or the feed-rate override).
• SINUMERIK 840D / 828D UAFEHL Alarm — the PLC stop alarm on Siemens controls: what UAFEHL means, why the PLC halts, and the usual triggers (I/O module, drive enable, safe-integration).
• FANUC 0i-Mate / 0i-D Alarm Quick Reference — same number, different meaning across series — including the 950/960 traps and the FSSB 5134–5198 range.
• SINUMERIK 828D Alarm 2000 / 2001: PLC Sign-of-Life Monitoring — what the sign-of-life alarm actually monitors on the 828D, and where to look first.
• Mitsubishi M80 / M70 Servo Parameters #2201–#2210 — the full servo parameter table for M80/M70 in one place.
• Mitsubishi M80 / M70 Alarm Codes: M01 / S / Y / Z / AL Families — how the M80/M70 alarm families are grouped, and which ones point at the drive rather than the program.
• SINUMERIK 828D NCK Battery Alarm 2100/2101/2102 — replace live or power down, what data is lost, and how the fan/battery module comes out.
• Heidenhain TNC Error Code List: How to Read 6-Digit Codes — the structure of 6-digit TNC errors and the high-frequency families worth memorising.
• Heidenhain Touch Probe Calibration: iTNC 530 vs TNC 640 — two generations, two systems — MP numbers on iTNC 530, Cfg on TNC 640 and later.
• Heidenhain TCH PROBE 31 / 481 Tool Length Measurement: MP vs Cfg — the two cycle formats (31.x four lines vs 481 one line of Q parameters), the three Q340 modes, Q260 clearance height with the MP6540 vs safetyDistStylus safety zone, and the 99 vs 20 individual-tooth limits.
• Fanuc G41/G42 Interference Alarm: The 2×TNR Rule — the minimum radial step rule behind most cutter-compensation interference alarms.
• Used CNC Machine Electrical Inspection Checklist — 30 Checks — for buyers: what to check before money changes hands, and the common ways faults get concealed.
• SINUMERIK 828D User Alarm Bits: DB1600 Sequential Mapping — the sequential bit-to-alarm mapping and how it differs from the 840D grouped scheme.
• SINUMERIK 828D Extended User Alarms 701000–701999: DB9913 Config — configuring DB9913 and the compatibility-mode checkbox that blocks it.
• SINUMERIK 828D Semi-Closed Loop Conversion: MD, PLC Bits, Backlash — the three layers — NC machine data, PLC interface bits and backlash compensation — that must move together.
• SinuTrain for SINUMERIK Operate: Install, Program, Simulate — install the Siemens PC simulator on Windows 10/11 and prove programs offline before the machine is tied up.
• SINUMERIK 828D PLC Programming Tool — install, connect and back up the 828D PLC program: LAD/FBD/STL editing, online monitoring, Upload Station to PG, and where to get the software legitimately.
• FANUC Servo Amplifier Replacement: Discharge, Teardown, Motor ID, Verification — the full swap procedure: power-off and discharge, teardown order, motor ID No.2020 write-back and the three post-swap checks.
• FANUC SV0381/0384/0385/0386/0387 Servo Alarms: Poor Grounding and the Linear Scale (EXT) Alarm Family — when these alarms trip on a full-closed-loop machine, the root cause is usually noise and bad grounding, not a dead scale; covers the signal chain, SDU, 4 noise paths, official shielding rules, and the 1815#1 semi-closed isolation test.
• FANUC Program Transfer: RS-232, Memory Card, USB, Ethernet and DNC — the DB9-DB25 pinout, the 0020 I/O channel with the 0101/0102/0103 frame parameters, media format limits by generation, FOCAS2 port 8193 with the FTP transfer screen, and the 073/085/086/087 alarm table.
• FANUC Program Transfer Tool V18 — install, register and wire the Ethernet link: IP planning, CNC-side FOCAS2 ports 8193/8192, session setup and drag-and-drop program transfer.

6. How to Use These Guides

• The alarm text on your screen is always authoritative. Messages, descriptions and parameter numbers vary by FANUC series, installed options and software version. Where a guide lists a parameter number, confirm it on your machine before changing anything.
• Back up before you change anything. Parameters, PMC program and ladder — and verify the backup can actually be read back.
• Classify before you adjust. Especially for servo problems: high-frequency squeal, low-frequency flutter, start/stop overshoot and machining ripple have opposite handling directions. Getting it backwards makes it worse the more you tune.
• Suspect the machine before suspecting the parameters. Guide after guide in this section repeats it, because it is the most common way field time gets wasted.

Disclaimer: These guides are a personal compilation organized from FANUC documentation and field experience. Always follow the official manual for your machine and verify by measurement on site. Operations involving safety functions must follow the relevant procedures and be performed by suitably qualified personnel.

Which guide do I need?

I’m new to FANUC PMC — where should I start?

Read FANUC PMC Ladder Diagram Beginner Tutorial first — it covers what a PMC is, the difference between sequential execution and relay logic, and the basic instruction set, with two complete worked examples. Once you can read a ladder, move to FANUC PMC Project From Scratch for the process of delivering a real project.

My machine shows an alarm number — where do I look it up?

Use the six-part FANUC Alarm Code List, split by range: Part 1 covers 0001–0224, Part 2 0230–0461, Part 3 0492–1308, Part 4 1332–1973, Part 5 2032–5110 and Part 6 5130–5559. Find your number in the left column and read the message plus the first action. If your alarm is a servo alarm in the SV range rather than a P/S number, the servo guides in section 3 are a better starting point.

My machine has no alarm but the program won’t advance — which guide?

Use FANUC No-Alarm Fault Diagnosis. It maps the three usual causes to specific diagnosis numbers: DGN000 means the system is waiting for the M-code completion signal, DGN003 means the in-position check is not passing, and DGN005 means an axis interlock is active. Keep FANUC Diagnosis Numbers Quick Reference open alongside it.

Servo vibration or overshoot — which article should I read?

Both servo guides apply, but they solve different problems. Read CNC Servo Vibration, Overshoot and Noise first to classify what you are actually seeing — high-frequency squeal, low-frequency flutter, start/stop overshoot or machining ripple — because the handling directions are opposite. Then use FANUC Servo Gain 2021 / 1825 Adjustment for the actual parameter values, the inertia-ratio formula and the adjustment sequence.

All three sections