Hardinge CNC Fault Codes — Complete Troubleshooting Guide

Hardinge CNC machines — the GS-series precision lathes, Bridgeport VMC series, and HQS/HQR horizontal turning centers — use Fanuc and Siemens controls layered on top of Hardinge-specific PMC (Programmable Machine Controller) logic. That two-layer alarm structure means a single fault can generate both a Fanuc system alarm and a Hardinge PMC alarm at the same time. This guide covers both layers so you can stop chasing symptoms and fix the root cause.

How Hardinge Alarm Numbering Works

Hardinge machines running Fanuc controls display alarms in several ranges:

PMC alarms (1000+) are generated by Hardinge’s ladder logic, not Fanuc. They appear on the message screen as text strings. To see them: press [MESSAGE] → [ALARM] tab on the Fanuc MDI panel.

Accessing Alarm History

Before clearing any alarm, check history to see the sequence of events:

1. Press [MESSAGE] on the MDI panel
2. Select the [ALARM] soft key
3. Press [HISTORY] or page down to the alarm log
4. Record all alarms — not just the most recent one
5. Note the time stamps; alarms that appear in clusters indicate a cascade failure

On machines running Fanuc 31i or newer: the alarm history holds the last 100 alarms with timestamps. On older 18T/21i systems, history is limited to the last 10 alarms.

Servo Alarms (400–499)

Alarm 401 — Servo Not Ready

Meaning: The servo amplifier has not completed its ready sequence. The CNC sent a command but the drive did not acknowledge.

Causes:

• Servo drive emergency stop input still active
• DC bus in the servo amplifier not fully charged
• Servo amplifier hardware fault
• Loose or missing 24V control power to the servo rack

Diagnosis:

1. Check the servo rack — look for a red LED on any amplifier module
2. Verify 24VDC control power at the servo amplifier terminal block (typically TB1)
3. Cycle power with a 30-second wait before restart — the DC bus needs time to discharge and recharge
4. If the alarm returns immediately on power-up, the amplifier is faulted; check the amplifier’s own LED fault code

Fix: If the amplifier LED shows no fault and 24V is present, suspect an emergency stop relay that did not release. On GS-series lathes, there is a dual-channel E-stop monitoring relay in the main electrical cabinet — test both channels.

Alarm 408 — Servo Alarm: Serial Not Ready

Meaning: Serial communication between the Fanuc CNC and the digital servo amplifier has failed or the servo drive reports it is not in a ready state.

Causes:

• Corrupted or incorrect servo parameters (8100-series on 18T, 2000-series on 31i)
• Servo amplifier hardware fault
• Fiber optic FSSB cable damaged or disconnected (on systems using FSSB)
• Power restored but parameters lost or reset to default

Diagnosis:

1. Check parameters 8120, 8220, 8320 (18T) or equivalent — these must contain valid motor numbers (1–14) that match the actual servo motor installed
2. On FSSB systems: inspect the fiber optic cable running from the CNC main board to the first amplifier in the chain
3. Check for “SV” errors in the amplifier display

Fix: If parameters were corrupted (e.g., after battery failure or an intentional parameter clear), you must re-enter servo motor parameters from the machine-specific parameter sheet. Hardinge customer service can provide factory parameter files — request them with your machine serial number.

Parts needed: Hardinge servo parameter backup (paper or electronic), replacement FSSB fiber cable if damaged (Fanuc A66L-6001-0026 series)

Alarms 417/427/437 — Servo Alarm: X/Z/3rd Axis Digital Parameter

Meaning: The Fanuc control cannot communicate correctly with the digital servo amplifier for the named axis. This specific triplet (417, 427, 437) almost always means servo motor parameters are missing or wrong.

Causes:

• Parameter file corrupted or lost (most common: after holding DELETE on power-up)
• Wrong motor number entered in axis parameter block
• Servo amplifier replaced but not re-parametrized

Diagnosis:

1. Go to [SYSTEM] → [PARAM] and check parameters 8120 (X axis), 8220 (Z axis), 8320 (3rd axis)
2. Each must have a non-zero value (1–14) corresponding to the motor installed
3. Also verify parameter 0001 bit 0 and 7001 bit 0 are both set to 1 for inch machines

Fix: Enter correct motor numbers. If you don’t have the parameter sheet, pull the motor nameplate part numbers, cross-reference in the Fanuc servo motor parameter manual, and enter the matching ID. After entry, power cycle — the control will automatically load the correct gain and current parameters for that motor.

Alarm 436 — Servo Alarm: X Axis Overload

Meaning: The X-axis servo motor or drive detected excessive current draw, indicating mechanical overload.

Causes:

• Worn or contaminated linear guides (ways)
• Turret or toolholder collision
• Loose coupling between servo motor and ball screw
• Ball screw gunked up with chip contamination (most common on GS-series)
• Incorrect cutting parameters generating excessive force

Diagnosis:

1. Manually jog X axis slowly — listen for grinding, feel for resistance
2. Check ball screw and linear guide surfaces for chip contamination or scoring
3. Verify the coupling between motor and ball screw is tight
4. Check servo load meter during a dry run — load should stay below 80%

Fix: Clean and re-lubricate the ball screw and linear guides. On GS-42/51/65 lathes, the lubrication pump cycle interval is factory-set — verify it is operating on schedule. Hardinge specifies Mobil Vactra No. 2 way oil for most GS-series machines.

Spindle Alarms (700–749)

Alarm 749 — Spindle Drive Fault

Meaning: The spindle amplifier has detected a fault condition. This is a generic wrapper — the actual cause is identified by the LED code on the spindle drive itself.

Causes (matched to spindle amplifier LED codes):

• AL-01: Motor overheat — insufficient spindle cooling, excessive duty cycle
• AL-02: Excessive speed deviation — belt slip (on belt-drive spindles), tool overload
• AL-06: Overspeed — speed command error or encoder malfunction
• AL-09: Excessive DC bus load — regenerative braking circuit failure
• AL-24: Serial transfer error — fiber optic spindle communication cable issue
• AL-27: Position coder disconnection — orientation/rigid tap encoder cable failure

Diagnosis:

1. Read the LED code on the spindle amplifier — this is the primary diagnostic
2. For AL-01: check spindle motor cooling fan operation (listen for it), verify coolant flow to spindle nose if liquid-cooled
3. For AL-24: inspect fiber optic cables from CNC to spindle amplifier
4. For AL-27: check the position coder cable connector at the spindle motor

Fix: Address based on the amplifier LED code. AL-27 on Hardinge machines is frequently caused by a damaged connector at the position coder — the connector is exposed to chips and coolant. Clean with contact cleaner and reseat.

Parts needed: Fanuc spindle position coder (A860-0308-T301 or machine-specific equivalent), spindle motor cooling fan replacement

Alarm 1000-series: Hardinge PMC Spindle Alarms

These are generated by Hardinge ladder logic and appear as text messages:

Collet and Chuck Alarms (2000-series PMC)

PMC Alarm 1001 / 2001 — Collet Chuck Fault

Meaning: The collet closer did not reach the commanded position (open or closed) within the allowed time, or the draw tube position is inconsistent with the commanded state.

Causes:

• Draw tube proximity switches out of adjustment or failed
• Insufficient air or hydraulic pressure to the collet closer actuator
• Mechanical jam in the collet closer (collet closed on itself without stock)
• Incorrect parameter for draw tube travel direction

Diagnosis:

1. Identify the two draw tube proximity switches — typically mounted on a bracket near the spindle rear
2. With the machine in MDI mode (spindle stopped), command collet open and watch both prox switch LEDs
3. One LED should illuminate when fully open, the other when fully closed
4. If neither switches at the expected position, adjust the switch bracket or check for a mechanical obstruction

Fix: On GS-series lathes, if the collet was commanded closed without a collet or stock in place, the draw tube may have traveled past its normal range. Command “open” via the chuck/collet button to reverse direction. If the draw tube is fully retracted and the machine shows “open,” a parameter controls draw direction — check the machine parameter sheet for the collet direction bit.

Parts needed: Draw tube proximity switch (Turck or Pepperl+Fuchs M12 style, machine-specific), collet closer actuator rebuild kit

PMC Alarm — Collet/Chuck Open During Spindle Run

Meaning: The control detected the chuck-open signal while the spindle was running (or commanded to run). This is an interlock, not a malfunction.

Causes:

• Chuck-open proximity switch failed in the active state
• Chuck or collet is actually open (part not loaded, bar end reached)
• Wiring short on the chuck open input circuit

Diagnosis:

1. Go to [SYSTEM] → [DIAGN] (PMC diagnostics) and monitor the chuck open input signal address (consult machine electrical drawings for the specific address)
2. If the signal shows “1” (active) when the chuck is visually closed, the prox switch is failed or misadjusted

Bar Feeder Interface Faults (5000-series PMC)

Hardinge GS-series machines are commonly paired with LNS, FMB Turbo, or Iemca bar feeders. The bar feeder communicates with the Hardinge PMC via a discrete I/O interface or RS-232 serial link. Faults in this interface appear as PMC alarms.

PMC Alarm — Bar Feeder Communication Fault

Meaning: The Hardinge PMC is not receiving expected signals from the bar feeder, or the handshake sequence timed out.

Causes:

• Bar feeder powered off or E-stopped
• Interface cable disconnected (typically a 25-pin D-sub or M23 connector at the back of the lathe)
• Bar feeder internal fault preventing response
• Mismatched interface parameters (baud rate, signal levels for serial interfaces)

Diagnosis:

1. Verify the bar feeder is powered on and showing its own ready state
2. Inspect the interface cable at both ends — this cable runs along the floor and is frequently damaged
3. On machines with RS-232 interface: check baud rate matches (typically 9600 baud)
4. Monitor bar feeder request/acknowledge signals in the Hardinge PMC diagnostics screen

Fix: Most interface problems are cable-related. Replace the interface cable with a shielded cable. If using a discrete I/O interface, verify +24V is present at the bar feeder I/O connector from the machine side.

PMC Alarm — End of Bar / Bar Finished

Meaning: The bar feeder has signaled that the bar stock is exhausted (end-of-bar position reached). This is typically a normal production condition, not a fault.

Causes (if unexpected):

• End-of-bar sensor on the bar feeder adjusted too early
• Short bar stock loaded
• Bar slip in the pushrod gripper

Fix: Load new bar stock. If triggering prematurely, adjust the end-of-bar sensor position on the bar feeder per the bar feeder’s service manual.

Parts Catcher Faults

PMC Alarm — Parts Catcher Fault / Timeout

Meaning: The parts catcher did not reach its commanded position (catch or retract) within the programmed timeout.

Causes:

• Air pressure insufficient (min 80 PSI required by most Hardinge parts catchers)
• Parts catcher extend/retract proximity switches out of adjustment
• Mechanical jam (chips built up in the catcher mechanism)
• Air solenoid valve failed

Diagnosis:

1. Manually command parts catcher extend and retract via MDI M-codes (typically M78/M79 or machine-specific M-codes — check the Hardinge programming manual)
2. Watch the catcher mechanism — does it move?
3. If it doesn’t move: check air supply and listen for the solenoid valve clicking
4. If it moves but the alarm persists: adjust the proximity switches

Fix: Clean chip buildup from the catcher tray and pivot mechanism. Verify proximity switch mounting screws are tight — vibration loosens them over time.

Parts needed: Parts catcher air solenoid valve (machine-specific), M12 proximity switch for position detection

Axis Overtravel Alarms (100–199)

Alarm 100–199 — Overtravel

Meaning: An axis has reached or exceeded its software or hardware travel limit.

Causes:

• Work offset or tool offset wrong, placing commanded position outside machine travel
• Machine reference (zero) position lost after a power failure
• G92 or G50 work shift active from a previous program
• Actual mechanical travel limit tripped

Diagnosis:

1. Check current axis position display — is it showing a reasonable value?
2. Verify the work coordinate system origin makes sense for the part
3. Check for active G92/G50 shifts in the offset page

Fix for software overtravel:

1. In the MDI mode with feed hold: jog the axis back into the travel envelope (you may need to temporarily increase the soft limit parameter)
2. Clear the alarm with RESET
3. Correct the program or offset that caused the excursion

Fix for hardware overtravel:

1. The machine must be powered up in override mode — hold the overtravel release button while jogging the axis off the limit switch
2. After clearing: re-establish machine reference position (home)

Coolant Fault

PMC Alarm — Coolant Motor Overload

Meaning: The coolant pump motor thermal overload relay has tripped.

Causes:

• Coolant sump too low (pump running dry or cavitating)
• Coolant filter clogged, causing pump to overwork
• Coolant too viscous (concentration too high or wrong fluid for temperature)
• Coolant pump motor bearing failure

Diagnosis:

1. Locate the coolant pump motor thermal overload relay in the electrical cabinet (labeled OL or thermal relay on the panel drawing)
2. Check if the reset button has popped out
3. Check coolant level in the sump before resetting

Fix: Reset the thermal overload only after verifying the root cause. Running dry will destroy the pump seals quickly.

Accessing and Resetting Alarms

Standard Alarm Reset Procedure

1. Remove the cause of the alarm
2. Press [RESET] on the MDI panel
3. For PMC alarms requiring acknowledgment: some require pressing [RESET] twice or navigating to the PMC alarm screen

PMC Alarm Screen Access

1. [SYSTEM] → [PMC] (soft key) → [ALARM]
2. This shows active PMC alarms with their PMC address
3. Use this screen to trace the ladder logic if an alarm origin is unclear

Fanuc Alarm History

1. [MESSAGE] → [ALARM] → page down or [HISTORY] soft key
2. Records last 10–100 alarms with timestamps (version-dependent)

Hardinge-Specific Maintenance Intervals

Parts Reference Table

Quick Diagnostic Reference

When Hardinge technical support is needed, have the machine serial number (plate on the headstock), the control software version (visible on the Fanuc boot screen), and the complete alarm history ready before calling.

Where to Buy Replacement Parts

Find replacement parts for Hardinge CNC lathes on Amazon:

• Hardinge CNC Machine Parts
• Fanuc Servo Motor Encoder Cable Replacement
• CNC Spindle Bearing Replacement