For machinists and CNC programmers, G-code is the language of the shop floor. Every hole drilled, every contour milled, and every part finished comes down to a carefully written sequence of commands. But even experienced professionals occasionally run into error codes. Understanding what those codes mean — and how to fix them — is essential to keeping production on schedule, avoiding scrap, and staying safe.
This article explains some of the most common G-code error codes, how to troubleshoot them, and when it’s best to simply press the reset button. Along the way, we’ll touch on career paths for those interested in machine shop jobs hiring near me, conversational machinist jobs, or shops hiring for an experienced CNC programmer.
What G-Code Error Codes Are
G-code (sometimes called ISO code) tells a CNC machine how to move: where to position, how fast to feed, what tool to use, and so on. Every CNC control has its own variation — Fanuc, Haas, Siemens, Heidenhain — but all give feedback when something’s wrong.
An error code is essentially the control’s way of saying, “I don’t understand” or “Something’s not safe.” Some codes simply stop execution; others cause alarms that must be cleared. Recognising the meaning behind the code saves time and material.
Common Error Codes and How to Fix Them
Below are some of the error or alarm codes machinists see most often, along with practical fixes:
1. Feed Hold or Feedrate Override Alarms
- What it means: The feedrate has been overridden too low or the control detected an unsafe feed.
- How to fix: Check the feedrate override dial; set it back to 100%. Verify the programmed feed (F word) in the block. Reset the alarm and re-run.
2. Spindle Speed Mismatch
- What it means: The spindle speed (S word) in the G-code conflicts with machine limits.
- How to fix: Open the program, locate the line with the offending S value, and ensure it’s within the allowable RPM range. If needed, adjust tooling to suit the correct speed.
3. Tool Change Alarm (M06 / T Code)
- What it means: The requested tool isn’t loaded or the magazine is out of sync.
- How to fix: Verify the tool number in the program matches the carousel. Manually index the magazine if necessary. Check that tool offsets are properly set.
4. Overtravel or Soft Limit Alarms
- What it means: The machine tried to move beyond its limits.
- How to fix: Confirm work offsets (G54–G59) and tool lengths. Simulate the path in graphics if available. Adjust coordinates or fixtures to avoid hitting limits.
5. Missing or Invalid G-Code Command
- What it means: The control received an unsupported or out-of-sequence G-code.
- How to fix: Look for typos (e.g., “G0O” instead of “G00”). Make sure modal codes are set before executing certain operations.
6. Arc Radius Error (G02 / G03)
- What it means: The start point, end point, and radius don’t match mathematically.
- How to fix: Recalculate the arc radius or use I, J, K values for centre points. Some controls need a specific plane (G17, G18, G19) before arcs.
7. Subprogram Call Error (M98 / M99)
- What it means: The program tried to call a subprogram that doesn’t exist or is mis-numbered.
- How to fix: Confirm the subprogram number matches and is loaded in the control. Check for missing M99 returns.
8. Work Offset Not Set
- What it means: The machine is referencing a coordinate system that hasn’t been zeroed.
- How to fix: Touch off the part, update G54 or whichever offset is in use, and re-run.
These are just a few examples. Most CNC controls have hundreds of possible alarms, but the troubleshooting pattern is the same: read the code, check the relevant part of the program, inspect machine settings, and verify tools and offsets.
When It’s Best to Press Reset
Sometimes, the fastest and safest fix is simply to hit the reset button. For example:
- After a tool breakage or unexpected crash, the control may be in a confused state.
- When multiple alarms appear in sequence, clearing and re-initialising can save time.
- If you’ve made edits on the fly and the machine won’t resume smoothly, resetting ensures modal states return to normal.
However, don’t rely on reset as a crutch. If the underlying cause isn’t addressed, you risk repeating the same error — or damaging the machine, tooling or part. A disciplined approach is: stop, diagnose, fix the code, then reset.
Building a Career in CNC Machining
For people who enjoy working with technology and precision, the machining trade offers stable and rewarding work. If you’re searching for machine shop jobs hiring near me, there are opportunities in both small job shops and large production facilities.
Shops are also expanding their use of conversational programming — controls where you fill in fields instead of writing long G-code manually. That’s why conversational machinist jobs are increasingly listed on specialist job boards. These roles require a solid grasp of machining fundamentals plus an understanding of how to navigate menus and on-screen prompts.
For more advanced positions, many companies are hiring for an experienced CNC programmer who can optimise tool paths, write post-processors and integrate CAD/CAM systems. The ability to diagnose G-code errors, reduce cycle time and improve part quality is highly valued.
If you’re looking for openings, one helpful resource is CNCShopJobs.com. Despite the name, it also posts skilled-trade positions across a variety of industries, including machining, CNC programming and maintenance. Whether you’re an entry-level operator or a seasoned programmer, you can browse listings and apply directly.
High-Resolution Images Enhance Understanding
Including high-resolution images of machinists at work makes an article like this come alive. Photos of technicians setting up CNC mills, inspecting parts with calipers, or programming at a control panel help readers visualise the environment. If possible, include shots of:
- A machinist loading a part into a vise or chuck
- Close-ups of the CNC control screen showing error messages
- A programmer editing G-code at a workstation
- Finished components being measured or deburred
These visuals reinforce the real-world context of G-code troubleshooting and the skills employers seek.
Conclusion
G-code is powerful but unforgiving. Even a small typo can trigger an alarm or ruin a part. By learning the most common error codes — feedrate issues, spindle speed mismatches, tool change errors, overtravel alarms, arc radius conflicts and more — machinists can quickly diagnose problems and keep production moving. And knowing when it’s best simply to press reset ensures the machine starts fresh without carrying over errors.
For anyone exploring career opportunities in this field — whether you’re searching for machine shop jobs hiring near me, interested in conversational machinist jobs, or applying where companies are hiring for an experienced CNC programmer — your ability to handle G-code errors will set you apart.
Check out the specialised listings at CNCShopJobs.com to find positions that match your skills. With solid troubleshooting habits and a keen eye for detail, you’ll be well-placed to succeed in the evolving world of CNC machining.
