ER303 - Switch activation error

Potential root cause

Troubleshooting steps

Broken flag

Check the left side of the print head housing. Ensure that the small tab at the side is still present and undamaged. When this part is damaged or broken off, the print head will reach the switch as expected, but it will not be activated.

If any defects are detected, this part of the print head housing may have to be replaced. If this is the case, please contact support or your local reseller for more information about spare parts and services.

Object in gantry system

Check if there are any obstructions in the gantry system that could prevent the print head from reaching the left side of the gantry. Manually move the print head. First, push the X beam to the back of the gantry, then slide the print head to the left. Alternatively, select the Home print head command in the Factor 4 menu (Maintenance → Print head).

If you feel any blockages, carefully inspect the gantry for any objects sticking out or damaged parts that may hinder the movement.

Loose belts

If the belts are very loose, the movement of the print head may not be accurate. The print head may not reach the X switch in the expected timeframe, or it may not move at all.

Check and retension the belts as described in this article: Factor 4 - Belt tension

Loose pulleys

If one or more of the pulleys in the gantry system are loose, the movement of the print head may not be accurate. The print head may not reach the X switch in the expected timeframe, or it may not move at all.

For the X switch error, particularly check the pulley connected to the X motor. This is located on the left side of the X beam. Tighten the set screw if this is loose.

Defective or disconnected X switch

If the print head flag is intact, there are no obstructions, and the head moves accurately (no loose belts or pulleys), then it is likely that the switch is disconnected or broken. Disassembly and potential part replacement are required to resolve the problem. Please contact support or your local reseller for further instructions or information about services.

Motor cable damaged

The motor cable on the gantry system is the grey flatwire on the left side. This cable connects both the X and Y motors to the main electronics, via the socket in the back left corner of the build chamber. If this cable is damaged or defective, one or both of the motors will not work at all or not as expected.

Check the cable for damage, particularly near the X motor (connector, and where it is secured under the bracket) and the connector at the back (that plugs into socket). Please notify support if any damage is detected.

Note: For further inspection of the cable, the gantry must be removed from the printer. Please contact support for advice and further instructions if the cable is the suspected root cause.

Potential root cause

Troubleshooting steps

Object in gantry system

Check if there are any obstructions in the gantry system that could prevent the print head from reaching the back of the gantry. Manually move the print head. First, push the X beam to the back of the gantry, then slide the print head to the left. Alternatively, select the Home print head command in the Factor 4 menu (Maintenance → Print head).

If you feel any blockages, carefully inspect the gantry for any objects sticking out or damaged parts that may hinder the movement. This includes, for example, the screws that secure the white plastic cover at the back of the gantry. If these are not properly tightened and stick out, this will block the X beam from moving fully to the back.

Tip: Ensure that the print head cables are properly secured to the Bowden tubes with the cable clips. If the cables are loose, they might sag down and get stuck between the X beam and the back of the motion system. This will prevent the switch from being activated and could damage the cable(s).

Loose belts

If the belts are very loose, the movement of the print head may not be accurate. The print head may not reach the Y switch in the expected timeframe, or it may not move at all. Check and retension the belts as described in this article: Factor 4 - Belt tension

Note: For any Factor 4 printer in use since before August 2025, it is recommended to firmly push the belt wedges in place. This reduces the chance of the belts losing tension over time. Find the instructions in the Belt tension support article.

Loose pulleys

If one or more of the pulleys in the gantry system are loose, the movement of the print head may not be accurate. The print head may not reach the Y switch in the expected timeframe, or it may not move at all.

For the Y switch error, particularly check the pulleys connected to the Y motor and the motion shaft. If any of the pulleys are loose, tighten the set screw.

The Y motor is in the back left corner. There is a pulley on the motor, and a short belt connects this to the gear ratio pulley on the motion shaft. The pulleys on the motion shaft are harder to reach. The one on the right side is accessible, but the one on the right is located under the Y motor. You will have to remove the gantry module to access it. Visit this page for instructions or contact support or your local reseller for more information.

Skewed X beam

If the X beam in the gantry system is skewed, the movements will not be accurate. This may cause the X beam flag to miss the Y optical switch. This may have occurred after a print failure, such as a collision of the print head and layer shifts.

To check this, manually move the X beam to the back of the gantry system. There is a small metal corner protruding through the white plastic back cover. These corners function as mechanical end stops. With the X beam all the way to the back, check that the beam touches this corner on both sides. If there is a gap on one side, the beam is skewed and must be manually recalibrated. Learn more about X beam skew and how to correct it in this article: Factor 4 - Skewed X beam

Note: Please always notify UltiMaker support or your reseller before starting repair processes.

Loose / moved switch PCB

If the switch is not secured properly, it can shift a little to the back of the gantry. This means that the flag on the X beam may not be able to activate the switch properly. Carefully feel if the switch PCB is loose. You might feel it move up and down somewhat; this means that it is not properly secured. In this case, or in case of doubt, remove the gantry from the printer to correct this.
Loosen (but do not remove) the two screws that secure the Y switch PCB. Move it as far as possible to the front of the gantry, and fully retighten the screws. Reinstall the gantry module in the Factor 4.

Motor cable damaged

The motor cable on the gantry system is the grey flatwire on the left side. This cable connects both the X and Y motors to the main electronics, via the socket in the back left corner of the build chamber. If this cable is damaged or defective, one or both of the motors will not work at all or not as expected.

Check the cable for damage, particularly near the X motor (connector, and where it is secured under the bracket) and the connector at the back (that plugs into socket). Please notify support if any damage is detected.

Note: For further inspection of the cable, the gantry must be removed from the printer. Please contact support for advice and further instructions if the cable is the suspected root cause.

Defective or disconnected Y switch

If there are no obstructions, the X beam moves correctly (no loose belts or pulleys), there is no skew in the X beam, and the switch PCB is secured properly, then it is likely that the switch is disconnected or broken. Disassembly and potential part replacement are required to resolve the problem. Please contact support or your local reseller for further instructions or information about services.

Broken flag

Check the back of the X beam. Ensure that the small metal tab is still present and undamaged. When this part is damaged or broken off, the print head will reach the switch as expected, but it will not be activated.

If any defects are detected, the X beam may have to be replaced. This is unlikely, as the X beam is made of sheet metal, but if this is the case, please contact support or your local reseller for more information about spare parts and services.

Potential root cause

Troubleshooting steps

Object under build plate

The most likely cause for Z switch activation errors is that there is something located under the build plate. If the object is too large, it will prevent the build plate from reaching the Z optical switch. Never keep any tools, print cores, prints, or other objects inside the Factor 4 build volume.

Blocked lead screw

If the lead screw of the Z motor is very dirty or there are pieces of filament stuck in it, this could prevent the build plate from moving correctly. If the build plate cannot be lowered completely due to a blocked lead screw, ER303 may appear. Clean and relubricate the lead screw, as described in this article.

Tip: Always keep the bottom of the build volume clean. Pieces of filament etc. can be wiped into the bottom tray bin, which can easily be removed to empty out.

Defective or disconnected Z motor

Check if the Z motor still moves when activated. Use the Move build plate option in the Maintenance menu. If the error shows again straight away without being able to observe any movement, try raising the build plate manually just before selecting Raise or Lower. Although the build plate will lower by itself due to gravity, you should be able to hear the Z motor if it is engaged.

Note: Make sure to keep hands clear of the build volume after using the Move build plate option.

If the Z motor is unresponsive, it may be disconnected or defective. Further troubleshooting requires some disassembly and potential part replacement. Please contact support or your local reseller for further instructions or information about services.

Defective or disconnected Z switch

If the back cover panel of the printer has recently been removed, it is possible that the Z sensor was accidentally disconnected. If so, remove the back cover panel again to reconnect it. If the back compartment was not accessed recently, this root cause is very unlikely.

If none of the other troubleshooting options have helped to resolve the Z switch error, the switch itself may be broken. Please contact support or your local reseller for further instructions or information about services.