What Causes the BLTouch Probing Failed Error? (How to Fix?)

Everyone in the 3D printing space sooner or later finds out that manually leveling the bed is not a fun process, specifically upon observing that the manual leveling does not yield reliable results after spending all that time and effort to get it as correctly as possible.

On the other hand, while the auto bed leveling sensors, such as the BLTouch, definitely offer a fantastic alternative to having to level the bed manually in terms of both consistency and user experience, getting them to work correctly can also be challenging at times.

Today, we will be going through one of the common errors you can face while using the BLTouch auto bed leveling sensor to level your 3D printer’s build plate, where the sensor cannot complete the probing sequence, and you can see the “Probing Failed” text on the screen.

So, what causes the BLTouch probing failed error?

Below, we have listed the potential reasons behind the BLTouch probing failed error:

  • The bed size is not configured correctly.
  • Travel limits are not configured correctly.
  • The probe offsets are not configured correctly.
  • There are mechanical problems regarding the BLTouch.
  • There are problems related to the wiring of the BLTouch.
  • The print bed is significantly unlevel.
  • The BLTouch probe is defective.

Next up, we will examine the factors that can cause the BLtouch probing failed error in greater detail and find out what we can do to fix this error as quickly as possible.

What Causes the BLTouch Probing Failed Error?

The BLTouch “probing failed” error is an issue that can occur during the probing sequence, where the sensor maps out the points on the build plate to gather the necessary data for leveling the bed correctly.

As a few different factors can be behind the BLTouch probing failed error, we have listed all the common issues along with descriptions that we believe will be helpful in identifying the problem in your case.

Here are the potential causes that can cause the BLTouch probing failed error and their explanations:

  • Misconfigured bed size in the firmware – The bed size parameters are responsible for the 3D printer to know how large the bed is, and their misconfiguration can cause BLTouch probing to fail as the BLTouch can end up at a location where there is no build plate.
  • Misconfigured travel limits in the firmware – Travel limit parameters are responsible for the 3D printer to calculate where the printhead can physically travel, and their misconfiguration can cause the BLTouch to fail the probing process due to the 3D printer trying to move the printhead to an impossible location.
  • Misconfigured probe offsets in the firmware – Probe offset parameters are responsible for telling the 3D printer where the BLTouch is located relative to the printhead, and their misconfiguration can cause the probing to fail by causing the BLTouch to end up in a location that doesn’t connect to the build plate.
  • Mechanical problems regarding the BLTouch – Issues with the movement of the BLTouch pin and the magnetic screw that holds it are the main culprits here, with incorrect mounting also being a possible reason.
  • Wiring problems related to the BLTouch – Incorrect wiring, defects in the wires, and even electrical interference can cause the BLTouch to fail the probing process.
  • Significantly unlevel print bed – When the print bed is way too unlevel, the BLTouch may crash into the print bed in some areas or not be able to reach the print bed at all, which can cause the probing process to fail.
  • Defective BLTouch probe – Finally, a defective BLTouch probe can cause the probing failed issue, especially if you have bought it from an unauthorized seller, which increases the likelihood of your BLTouch being a clone of sub-par quality.

While we have covered most of the common causes based on reports from the community, please note that this list may not be exhaustive, and in rare cases, the reason behind the BLTouch probing failed error in your case may not be in this list.

How to Fix the BLTouch Probing Failed Error?

The process of fixing the BLTouch “probing failed” error is primarily about going through the things that can potentially cause the problem and ensuring that everything is in order.

Below, we have prepared a step-by-step guide that provides solutions for the most common potential causes behind the BLTouch probing failed error:

  • Re-configure the bed size in the firmware. The X_BED_SIZE and Y_BED_SIZE parameters found in the Configuration.h file of the Marlin firmware should correspond to the X and Y dimensions of your build surface.
  • Re-configure the travel limits in the firmware. The X_MAX_POS, Y_MAX_POS, and Z_MAX_POS parameters found in the Configuration.h file of the Marlin firmware should correspond to the positions of the X, Y, and Z endstops of your 3D printer.
  • Re-configure the probe offsets in the firmware. The NOZZLE_TO_PROBE_OFFSET parameter found in the Configuration.h file of the Marlin firmware should correspond to the nozzle-to-probe offsets, where the X and Y positions refer to the X and Y distances between the probe and the nozzle, and the Z position refers to the Z-axis position of the printhead (relative to the home position) where the probe comes into contact with the build plate.
  • Maintain the BLTouch probe. The majority of the problems here are related to the BLTouch pin’s inability to move freely, which is why we recommend unscrewing the pin, ensuring that it’s not damaged and that its path is clear, re-magnetizing it and the inductive screw before putting them back in.
  • Re-do the wiring of the BLTouch. We highly recommend carefully following the BLTouch documentation for wiring and replacing the wires to be on the safe side.
  • Manually level the print bed. While the leveling doesn’t have to be perfect, a bed that is only slightly unlevel will make it much easier for the BLTouch to operate correctly as opposed to a bed that has a lot of height differences among different regions.
  • Force BLTouch SW Mode in the firmware. The BLTOUCH_FORCE_SW_MODE parameter in the Configuration_adv.h file of the Marlin firmware is responsible for the activation of SW mode.
  • Enable Z Safe Homing in the firmware. The Z_SAFE_HOMING parameter in the Configuration.h file of the Marlin firmware is responsible for activating Z safe homing.
  • Replace the BLTouch probe. The last resort solution is to replace the BLTouch probe you have, especially if you bought a clone or suspect that the probe you currently have is a clone with an original BLTouch from an authorized seller.

Please note that you will need to replace (re-flash) the firmware of your 3D printer with the modified one after making the firmware-related changes, as this is the only way to carry these changes over.

Wrapping Up

The BLTouch probing failed error is a frustrating issue that can arise at any time as a result of various factors, but in most cases, going through a list of solutions that address all the potential causes behind this error should solve the problem.

To recap, problems on the software side, such as the misconfiguration of parameters that are related to the operation of the BLTouch in the firmware, and hardware issues, such as mechanical problems and electrical problems regarding the BLTouch, or even an unlevel bed, can cause the BLTouch probing failed issue.

While correcting these software and hardware-related problems should fix the issue in most cases, activating extra safety features in the firmware, such as the SW mode or the Z safe homing, can also contribute to preventing this problem from occurring.

Happy printing!