Pro 5 homing error: cycle failed to clear limit switch

Suddenly my machine won’t initialize. I’m getting a GRBL Alarm 8: Homing fail: Cycle failed to clear limit switch when pulling off.

I saw other threads about loose ball screws, and i indeed did have a very loose on on the right y axis, i’ve tightened it up but still getting the error.

Here is the log:

N0 M5
Grbl 1.1h [‘$’ for help]
[MSG:‘$H’|‘$X’ to unlock]
Grbl 1.1h [‘$’ for help]
[MSG:‘$H’|‘$X’ to unlock]
[MSG:Caution: Unlocked]
N0 M5


Usually this is electronic: bad homing switch or loose connection, or mechanical: something prevents or interferes with machine motion — write in to

Sure thing, left a vmail and sent in an email with a screenshot. Thanks. Hopefully simple fix, it was working this morning, then I spun my machine 180 (the cart it’s on) and loaded a sheet of plywood to run a program.

I checked all the wiring and everything looks fine, so not sure what happened. Checked all the rest of the ball screws and motors as well.

This particular message means that the limit switch is stuck ON. Carbide Motion can show you the Inputs, from that you can tell which switch is stuck, and you can see if something has shifted and is triggering the switch.

1 Like

I wasn’t clear on where in motion you can see the switch status?
EDIT: finally figured that out

I might have tweaked something loading the 4x8 sheet, I’m gonna take it off and check square again.

So looks like my Y2 sensor is bad, it will show red when i test it but i’m not seeing it register.

I’m trying to follow the instructions to bypass it, however i cannot access the jog screen.

Bypassing Homing Switches

When a switch fails, it’s impossible to continue using the CNC machine, even though the homing switches are only used to initialize the machine. We have a process outlined below to continue using your machine while waiting for a replacement.

  1. Connect to your machine in Carbide Motion.
  2. Go to the MDI screen.
  3. Enter G28.3 and send it to the machine. This will cause your machine to set itself as “homed” with the current position being the home position.
  4. Go to the Jog screen.
  5. Jog your machine all the way to the back right, and lift the Z to the maximum height.
  6. Go to the MDI screen.
  7. Enter G28.3 and send it to the machine. This sets the current position as home, which should be very close to the real home position.

Note: You’ll want to reset your project zero after a manual homing routing because the manual home position will likely be just slightly off from the one your machine uses.

Furthermore i’ve traced the issue down to the control board, i checked the wiring harness for continuity all the back to the main connector harness plugged into the board.

Hopefully i hear from support tomorrow. I have a bunch of projects stacked up now!

I am experiencing a similar issue right now and looking forward to try your homing override method to get it running while waiting. My “X” homing fails. I have a new sensor in hand but did not take care of the issue. I am suspecting control board failure also.

G28.3 works, you have to disable bitsetter.

Trying to figure out if i can find a way to run my projects so i don’t get behind this week until parts show up.

I got my replacement board and wiring harness on Friday. Was able to run a job Saturday with tool changes. Hopefully no more issues.

1 Like

I have the same issue. They sent me a version 4 controller for my 5 pro because it wouldn’t control the VFD spindle or recognize the BitSetter. The new board does recognize these now, but when it intializes I get the GRBL Alarm 8 message. In the debug setting screen, it shows that Y and Y2 are triggered despite the fact the red indicator lights are off. If I put an allen wrench in front of those limit switches, they light up and shut off like they are supposed to.

I can still make cuts if I do the G28.3 that @cnackers mentions above, but thay is just a workaround. I can undo that setting by sending /$RST=$ in the MDI window and it MIGHT intialize once but it isnt consistent.

I know it isnt the limit switches because i have swapped the and when I put the old controller board back on it initializes every time.

I ran the VFD spindle control cable down the same track as the data cables so that I could keep everything on one side. I will move that and test the cable going the other way and see if it helps.

Any other suggestions are welcomed.

Sucks there seems to be a bad batch of boards or something, would be nice if they acknowledged it.

Looks like a number of people have had issues lately and all were newer orders in the last couple months.

I have been fine since everything got replaced.


I just got the Rev 4 controller today too and am now running into this same issue. Home X and Home Y2 are stuck on even though the red lights on the limit switches are off. I reconnected the Rev 2.0 controller and everything works like it’s supposed to. I think there’s something wrong with the Rev 4.0 controller.


Yeah, I received mine back in June. have been working with CS to address the Bitsetter issue for almost 4 months and now this stuck limit switch indicator in CM. what’s next?

I’ve been getting this same thing intermittently on a new 5 Pro. Shutting off power, unplugging the motor and limit connections, reseating and turning it all back on has usually fixed it.

Z seems to home fine, but the second it tries to move back to the corner it errors out.

1 Like

If i leave mine off for about 5 minutes and unplug the USB cable from my PC, it resolves the issue for the moment. From my experience, this seems like a capcitor issue in the controll board needing time to discharge as this didnt happen with the previous controller board.

They sent me a new wiring harness to remedy the issue but that didnt help. Now I have to call them again.

I still have the original controller board and if it didnt have an issue with the VFD and BitSetter, Inwould use that one as it homes perfectly. I mentioned this to support but they wanted to replace the harness anyway. They even had me try the beta version of Carbide Motion which didn’t seem to change the homing behavior ata all.

I will post the fix if we ever figure it out.

1 Like

Well… I guess I get to join the club, I received a wiring harness replacement last Thursday. After replacing it I kept getting the same issues. Disconnected everything until this morning when customer service called and we went through it together. At first, setting up as new machine and initializing worked. Honestly, that made me even more concerned since it tells me is intermittent. So we went through the process again with customer support, and sure enough, this time the error showed up again. One more time, and this time it worked after pushing the X all the way forward.

Customer support told me to get a job going and get back to them to let them know if anything goes wrong. Attempting to start my first job and I think the machine thought it was in a different location??!! Stopped abruptly. So I thought, let’s go through the initialization again. No luck, homing error came back. Went through initial configuration a few times and no luck.

As you all can imagine, this is a little frustrating and disappointing to say the least. I would like to think I made the right decision here.

1 Like

I completely Stopped messing with bitsetter and life is better. Until they come up with a software patch etc. its useless to me. Make life easy on yourself and just manually set zeroes etc and start making things. I have been productive all day without bitsetter.

Bitsetter and bitzero are 2 different things. Without the bitsetter you need a different program for every tool so that you can redefine zero.

EDIT: sorry, I said “without the bitzero” in the post above originally. It has been corrected now.

1 Like

Find your center and run zero from top surface