What Does the Blue Light on the BLTouch Mean? (Solved!)

Please note that the technical information on this article is based upon the documentation for BLTouch version 3 and may not apply to other versions of BLTouch.

The BLTouch auto bed leveling sensor is, without a doubt, one of the most effective improvements to the 3D printing process as it provides an effortless and reliable way to level the bed without having to go through the horrors of the manual bed leveling process.

On the other hand, just as with any other piece of electronic equipment, the BLTouch needs to be correctly wired and configured before it can work correctly, and as it’s a simple piece of equipment that doesn’t feature a digital display, the only way for it to communicate with us is through the two LED lights it features.

Today, we will take a look at the blue light portion, in particular, of the BLTouch interface that features a blue and a red LED light and learn what the blue light signifies for the operating status of the BLTouch sensor.

So, what does the blue light on the BLTouch mean?

While the state of the blue light on the BLTouch doesn’t tell the whole story about the sensor’s operating status, the blue light shining very faintly does give us the information that we have correctly installed the PWM (pulse-width modulation) wire.

Next up, we will take a deeper look into the purpose of the blue light on the BLTouch, and find out what different states of the blue light, such as when it’s entirely on or entirely off, say about the sensor’s operational status.

What Does the Blue Light on the BLTouch Mean?

If you look at the BLTouch while it’s operating, you will notice the existence of two red and blue LED lights that shine in different patterns and brightness levels.

As the blue light on the BLTouch is only half of the interface, looking at the blue light alone doesn’t give us a lot of information about whether the BLTouch is operational or not.

On the other hand, we can get one piece of information from the blue light of the BLTouch, which is the fact that the PWM (pulse-width modulation) wire (orange wire) is working as intended.

In the standard operating condition of the BLTouch, the blue light should shine faintly or blink in conjunction with the red light based on the action it’s taking, but as it’s very faint, you most likely won’t be able to notice the blue light unless you look closely.

Here are some of the BLTouch actions and the corresponding blue light (and red light) states, which shows all the possible things that the state of the BLTouch blue light can mean:

  • Self-test – Blue & Red
  • Alarm – No Blue & Blinking Red
  • Alarm release & Pin up – Blue & Red
  • Pin down – Blue only
  • Pin up – Blue & Red

BLTouch Blue Light Only – What Does It Mean?

The first case we will look at is when the blue light of the BLTouch sensor is shining while the red light is entirely off, which tells us a vital piece of information about the state of the sensor.

The scenario where only the blue light of the BLTouch is on while the red stays off means that the BLTouch isn’t operating as intended and most likely won’t perform the bed leveling process or respond to any commands until the problem is solved.

While the blue light being on while the red light stays off usually points towards issues with the wiring, with the 5V wire being the most common culprit, it could also mean that the BLTouch sensor itself isn’t functional anymore.

BLTouch No Blue Light – What Does It Mean?

The BLTouch blue light not shining is also a possible scenario that can happen while the red LED is in any possible state, but the message remains the same regardless of the red LED’s state.

The explanation behind the blue light of the BLTouch not shining at all is the most straightforward one out of all, as it simply means that you haven’t installed the PWM wire correctly.

As long as the PWM wire is working as intended, the blue light of the BLTouch should shine (albeit very faintly), even if there are other issues that are stopping the sensor from operating.

The PWM wire is the orange-colored wire of the BLTouch, which is the wire responsible for transmitting the control signal to the sensor. 

BLTouch Blue Light and Red Light at the Same Time – What Does It Mean?

Another possible combination for the BLTouch LEDs is when both the blue light and the red light shine together, which conveys another vital piece of information for the user.

The BLTouch blue light and red light shining at once mean that there is nothing to worry about, and the sensor is operating as it should since there are a fair few commands that can invoke this response from the BLTouch while it’s working.

Below, we have listed the scenarios where the blue light and the red light of the BLTouch shine at the same time, which gives us the entire picture of what this state can possibly mean:

  • Self-test
  • Alarm release
  • Pin up 

Wrapping Up

The blue light on the BLTouch sensor is one of the two LEDs that give us information about the state of the sensor, such as when it’s operational or when there is something wrong with its wiring that requires fixing before it can operate again.

To quickly recap, the only piece of information we can get from the blue light of the BLTouch alone is whether the PWM wire (orange wire) is operational or not, as the blue light won’t shine at all if there is an issue with this wire.

If the BLTouch is operating as intended, the blue light should shine faintly or blink depending on the action the sensor is performing, which usually isn’t too visible due to the bright red light overwhelming the blue.

Happy printing!