No alarm, the screen is on, but the axis does not move; you press JOG and the position does not change; you press Cycle Start and the program does not start. On a FANUC control, most of these cases are not a fault but a signal the control is waiting for. This guide condenses the “Troubleshooting” chapter (8.2–8.6) of the FANUC 0i-B and 0i-C maintenance manuals into an order an operator can follow. The aim is to read where the control is stuck from two screens before calling service: the status line and the DGN 000–015 diagnostic lines.
Step 1: Read the status line at the bottom of the screen
Below the position display the mode and state are shown. This line alone answers most questions:
| Shown | Meaning |
|---|---|
| EMG | Emergency stop signal active. The E-stop button, a door switch or a cabinet switch may be open. No motion is possible. |
| RESET | The control is in the reset state. An external reset signal is still present or the RESET key may be stuck. |
| JOG / HND / MDI / MEM / EDIT | The selected mode. If none is shown, no signal is coming from the mode switch. |
| **** | Automatic mode, program not started. |
| STRT | Program running; if the axis has still stopped, go to step 2. |
| HOLD | Feed hold pressed or the feed hold signal interrupted. |
| BAT | Battery low. Unrelated to motion, but the battery must be replaced. |
Clear EMG first, then confirm from the status line that the mode switch really selects the mode you want. If no mode name is shown, the problem is the mode switch or the PMC; the operator panel cable and switch are checked.
Step 2: Look at diagnostic lines DGN 000–015
On SYSTEM → [DGNOS], lines 000 to 015 show what the control is waiting for at that moment. The line showing 1 is the reason:
| DGN | Message | Meaning and action |
|---|---|---|
| 000 | WAITING FOR FIN SIGNAL | Waiting for the finish signal of an M, S, T or B code. The last auxiliary function in the program (for example M08, M19, a T code) has not completed on the machine side; check that function’s mechanical and electrical side. |
| 001 | MOTION | An axis move is being executed; normal. |
| 002 | DWELL | A G04 dwell is running; normal. |
| 003 | IN-POSITION CHECK | Positioning not complete: the position error (DGN 300) is not within the in-position width (parameter 1826). The servo may be straining; check 1825 servo loop gain (normally 3000) and the servo alarm history. |
| 004 | FEEDRATE OVERRIDE 0% | The feed override switch is at 0 %. Turn it up. |
| 005 | INTERLOCK / START LOCK | An interlock signal is active. The most common cause; explained separately below. |
| 006 | SPINDLE SPEED ARRIVAL CHECK | Waiting for the spindle to reach speed. The spindle is not turning or the speed arrival signal is missing. |
| 010 | PUNCHING | Data output in progress. |
| 011 | READING | Data input in progress. |
| 012 | WAITING FOR (UN)CLAMP | Waiting for an axis clamp/unclamp signal (rotary table, for example). |
| 013 | JOG FEEDRATE OVERRIDE 0% | The JOG feed override is at 0 %. Turn it up. |
| 014 | WAITING FOR RESET, ESP, RRW OFF | Reset, emergency stop or rewind signal still active. Go back to step 1. |
| 015 | EXTERNAL PROGRAM NUMBER SEARCH | External program search in progress. |
This table applies to both manual and automatic operation. If 001 or 003 stays at 1 while the axis is stopped, suspect the servo side; if it is 004, 005, 013 or 014, suspect the operator panel and interlock side.
Step 3: Where does the interlock (DGN 005 = 1) come from?
An interlock is a safety lock defined by the machine builder in the PMC program: door open, tool changer in an intermediate position, low air pressure, rotary table not unclamped, and so on. There are three kinds, and parameter 3003 shows which is in use:
- 3003#0 (ITL) = 0: the general interlock for all axes (*IT) is active.
- 3003#2 (ITX) = 0: the per-axis interlock (*ITn) is active.
- 3003#3 (DIT) = 0: the per-axis-and-direction interlock (±MITn) is active; on the T series it works only in manual operation.
What the operator can do: close the doors, bring the tool changer and rotary table back to their normal positions, check the air pressure, and consult the builder’s interlock list if there is one. On the PMC diagnostic screen (PMC → [PMCDGN] → [STATUS]), if the *IT bit at address G0008 is 0 the general interlock is present; that check is service level.
JOG does not work
In order:
- Does the status line say JOG? If not, the mode is not selected.
- If nothing happens when you press the axis direction key: if the direction key was already held before JOG mode was selected, the control does not see it; release and press again.
- Check DGN 013 (JOG override 0 %) and 005 (interlock).
- If the JOG feedrate parameter (1423) is 0 the axis will not move; compare with the builder’s value.
- On the T series, if the JRV bit of parameter 1402 is 1, JOG feed is defined per spindle revolution: the axis does not move unless the spindle turns. Start the spindle; if there is still no motion, the position coder cable is checked.
- On the M series the index table (B axis) cannot be moved with JOG, incremental or handwheel feed; that is normal.
- If machine lock (MLK) is on, the axis does not move and the position display does not update either; check the MACHINE LOCK switch on the operator panel.
Handwheel (HANDLE) does not work
- The status line must show HND.
- If the servo drive LED does not show “0”, the servo is not enabled; JOG will not work either, so look at the servo alarm first.
- Are the axis selector (X/Y/Z) and the multiplier switch (×1/×10/×100) in the right positions? At ×1 the step is 0.001 mm and may go unnoticed.
- 7102#0 (HNGx) sets the handwheel direction; 7110 is the number of handwheels in use (1–3). If the wheel runs backwards check 7102; if it does nothing check 7110 and the assignment of the I/O module the wheel is connected to.
- If the bits at the PMC’s X address count up and down when the wheel is turned, the wheel and cable are sound and the problem is in the assignment or a parameter; if they do not count, the wheel, cable (HA/HB signals, +5 V) or I/O module is faulty. That step is for service.
Automatic operation: the program does not start on Cycle Start
First make sure manual motion works; if not, the sections above take priority.
If the Cycle Start LED does not light (status line shows ****):
- The mode must be MEM, MDI or RMT; a program will not start in EDIT mode.
- The Cycle Start signal is processed when the key is released (on the 1-to-0 transition); holding the key is not enough, press and release.
- The feed hold signal (*SP) is normally 1; if the feed hold key is pressed or the signal is interrupted, no start takes place. Look for the HOLD indicator.
- Program protection or a door interlock may be locking automatic operation.
If the Cycle Start LED is lit but the axis does not move (STRT):
- DGN 000 = 1: waiting for an M/S/T code finish signal. Look at which block the program is stopped on; the M code has not found its response on the machine (for example the coolant pump overload has tripped, the tool changer cannot confirm its position).
- DGN 004 = 1: feed override 0 %.
- DGN 005 = 1: interlock or start lock (a separate signal on the T series).
- DGN 006 = 1: spindle has not reached speed; an S command was given but the spindle is not turning, or the speed arrival signal is missing.
- DGN 003 = 1: positioning cannot complete; if the axis cannot settle after G00, look at the servo alarms (400, 410, 411).
On some machines the first block is a G28 reference return or an M19 orientation; it may be the spindle, not the axis, that is being waited for. Running the program in SINGLE BLOCK to see which block it waits on is the quickest way.
The position display does not change but the motor can be heard
When machine lock (MLK) is on, axis commands are processed but there is no motion and the machine coordinate is not updated; check the MACHINE LOCK switch on the operator panel or the builder’s “axis lock” switch. Conversely, if the position changes but the axis really does not move, the coupling or the connection between motor and screw may have failed; stop immediately, this is a mechanical fault.
What to note before calling service
This is the manual’s own list and it shortens the service job considerably:
- When did it happen, how often has it recurred, was there a power cut or lightning?
- In which mode (JOG, MEM, MDI, REF) and on which block of the program?
- Only on one axis, and at every speed?
- What did the status line show, and which DGN 000–015 line was 1?
- What are the latest entries in the alarm history (SYSTEM → alarm history)?
- Control type, software edition, servo and spindle drive models (numbers starting with A06B).
Frequently asked questions
The axis does not move on my FANUC and there is no alarm. Where do I look first?
At the bottom line of the screen. EMG, RESET or a missing mode name are the first three causes. Then find the line showing 1 between 000 and 015 on SYSTEM → [DGNOS]; 005 interlock and 004/013 override 0 % are the most common.
What does DGN 005 INTERLOCK mean and how do I clear it?
A lock defined by the machine builder in the PMC is active: door, tool changer, air pressure, rotary table clamp and so on. The source of the lock is on the machine, not in a CNC parameter; consult the interlock list in the builder’s manual. Parameter 3003 only shows which type of interlock signal is used; it does not remove the lock.
I press Cycle Start, the LED flashes but the program does not advance?
The program has started and is waiting for a signal. DGN 000 (M code finish) and 006 (spindle speed arrival) are the most common causes. Run in single block to see which block it waits on, then check the machine-side response to the M or S code in that block.
JOG works but the handwheel does not. Why?
The servo is enabled (otherwise JOG would not work either). Check the axis selector and multiplier switches, parameter 7110 (number of handwheels) and the assignment of the I/O module the wheel is connected to. At ×1 the motion is very small; try ×100.
The machine does not move in REF mode either?
REF is also a manual mode; anything that stops JOG (EMG, interlock, override 0 %) stops REF too. In addition, the axis direction key must be held down for the reference return; motion stops when the key is released.
Mentor CNC Disclaimer and Safety Note: This content was prepared for training purposes from the troubleshooting chapter of the FANUC 0i-B and 0i-C maintenance manuals. Signal addresses, parameter numbers and screens vary with the control series and the machine builder’s PMC program. Interlock signals exist for safety; they must not be bridged or disabled. Work on the PMC diagnostic screen and parameter changes should be carried out by authorised service. Mentor CNC accepts no liability for damage arising from use of this material; the machine builder’s manual always takes precedence.