# Ender 3 BLTouch fails in assorted ways

My recently installed BLTouch probe regularly fails to perform ABL properly. There seem to be 3-4 failure modes:

1. Probe manages some points but fails partway through, with a "probing failed" message on the LCD screen, rendering it necessary to power-cycle the printer
2. Probe deploys on some point, then stows itself immediately, and treats that point as being a centimeter or two about where it actually is.
3. Probe completes all 9 points, then heats the nozzle in the back corner and never moves. The progress bar on the LCD counts up and eventually it claims to have finished the print, but the steppers (including the extruder) never move.
4. Probe flashes red throughout the cycle, which I believe means it failed a self-test probably because the mainboard started trying to speak to it before it was initialized, but occasionally when this occurs, it still works as expected.

For avoidance of doubt - sometimes it actually does work, and I get beautiful prints that adhere well during printing but are easily removed afterwards. And I have never had any issues with the Z homing using the probe, only the auto mesh levelling.

My setup:

• Creality Ender 3
• v1.1.4 mainboard with non-silent steppers
• genuine BLTouch v3, with official Creality pin27 kit
• Marlin 1.1.9 bugfix firmware, downloaded as hex file
• single iteration of probing
• 9 point levelling mesh
• Ultimaker Cura slicer 4.2.0
• Start G-code heats bed, homes G28, performs ABL G29, then heats nozzle (I don't have the actual G-code on my now as I'm away from my slicing computer)

[Related question: BL Touch Probing Fails Intermittently but answers do not apply as I am already using bugfix firmware and have checked all the cabling and connections]

• Have you ever managed to solve the issues? It appears you're not the only one with these kind of problems.
– 0scar
Jan 21 '20 at 6:34
• Unfortunately not - in the end I gave up and returned to manual tramming so I could actually get some printing done. Jan 21 '20 at 9:31
• Many thanks for your update, actually I'm experiencing the same, in my case it is caused by a defective touch sensor. I'll write an answer describing this. Switching sensor helped me.
– 0scar
Jan 21 '20 at 9:42

## 2 Answers

You had a faulty BLTouch. Mine experienced the EXACT same behavior and replacing it with a new BLTouch fixed the issue entirely (everything else I kept exactly the same, firmware etc), I simply swapped over the probe + cable with the new one.

When connecting the new BLTouch, make sure you wire the servos connector correctly. In my case with an SKR Mini E3 v1.2 I needed to switch the red wire with the blue wire. If you start the printer with the wires the wrong way around, it may cause damage. I suspect that is what happened to my original one.

• Welcome to SE.3D Printing, good answer, I experienced exactly the same, but then with non-genuine touch sensors, replacing them fixed the problem also.
– 0scar
Jan 23 '20 at 8:52

Connecting the bltouch or 3dtouch clone to the normal Z-endstop connector of a creality board (ender 3 / 3 pro / cr10) is the problem!

Creality added a capacitor to the Z-endstop connector to improve the signal of the normal endswitch. This capacitor impacts the data signal processing of the probe. (filters out signals)

Other boards / manufacturers often do not have this capacitor. So there is no problem when using the probe.

Known solutions:

1. connect the probe to the ISP header (data to MOSI, Ground to GND).

2. Others desolder the capacitor next to the Z-endstop-connector.

Here is described my "ISP header solution" with details... (for Klipper, but could be adopted for Marlin)

Further information on BLTouch Klipper docs (search for "Troubleshooting")

After fixing, Z should stop instantly when probe pin pops up. My probe speed is 50 mm/s (for Z). The Readability Check gives me 0.007-0.250 mm ranges between measurements (mine is a cheap Chinese clone).