Probe arm bending and probe failures
The G1 uses a mechanical probe (micro-switch) for automatic bed leveling. Two distinct failures are common: the rubber plunger getting stuck in the micro-switch, and the probe not triggering at all. Both prevent bed leveling from completing.
How the probe works
Section titled “How the probe works”The probe is a switch carried on an arm that is lowered and raised by a small servo motor. During probing the servo drops the switch down; when the switch contacts the bed it sends the trigger signal to Klipper; the servo then lifts it back up before the nozzle moves on. While down, the switch doubles as the Z endstop.
The servo connects to the board behind the extruder through a black 3-pin JST connector — a frequent fault point (see Failure 3). The printed arm is part E21, mounted on a factory-calibrated metal arm.
Failure 1 — Rubber plunger stuck in micro-switch
Section titled “Failure 1 — Rubber plunger stuck in micro-switch”Symptoms
Section titled “Symptoms”- Bed leveling starts but the printer moves down and crashes into the bed without stopping
- No trigger signal received — Klipper times out and reports a probe error
- The printer homes or probes correctly sometimes, but not consistently
The small rubber part inside the micro-switch mechanism gets stuck in the depressed position. It no longer springs back, so the switch stays “triggered” (or never triggers) even when the probe arm has lifted.
- With the printer powered off, locate the probe arm assembly
- Identify the black rubber plunger on the micro-switch
- Gently pull the rubber part outward until you feel it click back into its resting position
- If it doesn’t come out easily, try several gentle pulls — do not force it
- Power on, home the printer, and attempt bed leveling again
- If the problem recurs frequently: the micro-switch is worn → replace it
Failure 2 — Probe not triggering at all
Section titled “Failure 2 — Probe not triggering at all”Symptoms
Section titled “Symptoms”- Probe arm descends to the bed, makes contact, but Klipper reports “probe triggered before movement”
- Or: the probe arm descends past the bed surface (crash) with no trigger ever registered
The micro-switch itself has failed (internally open or shorted), or the wiring connection to the switch is broken.
- With the machine off, manually press the probe arm plunger by hand — you should hear a distinct click
- If no click: the micro-switch needs replacement
- If there is a click but it still doesn’t work: check the connector and wiring between the switch and the Octopus board
- Replace the micro-switch (Ginger Additive can provide the correct part)
Failure 3 — Probe drops randomly mid-print (wiring / connector fault)
Section titled “Failure 3 — Probe drops randomly mid-print (wiring / connector fault)”Symptoms
Section titled “Symptoms”- The probe arm descends unexpectedly during a print (not just during homing or bed leveling)
- The probe hits the bed or the already-printed object, gets stuck, and the machine reports a probe error or triggers an emergency stop
- Replacing the probe or the cable does not resolve the issue — it recurs on the next print
- The arm can be moved freely by hand without triggering, but it triggers mid-print
The black 3-pin JST connector that links the servo to the board behind the extruder makes poor contact. Even when it looks perfectly seated, the internal metal pins may not connect reliably. The intermittent signal makes the servo drop the probe at the wrong time — including mid-print, where it hits the print or drags across the bed. This is not a mechanical failure — the probe arm itself is fine.
A secondary cause: if there is plastic residue or drool under the nozzle before printing begins, the probe cannot reach the bed surface and the arm stays extended, leading to a false trigger as soon as the nozzle moves.
Fix — faulty servo connector
Section titled “Fix — faulty servo connector”- With the printer off, locate the black 3-pin JST connector between the servo and the extruder board (Klipper MCU extruder_board)
- Disconnect and re-seat it firmly — do this even if it looks fine, since the internal pins are the usual culprit
- If the connector or its pins are damaged or corroded, replace the connector / wiring — Ginger Additive can ship the correct cable
- After rewiring, test by manually moving the extruder head many times before starting a print — the probe should not extend at all during manual moves
- Run a test print while watching closely; the probe should only move during homing and bed leveling
Fix — nozzle drool blocking the probe
Section titled “Fix — nozzle drool blocking the probe”- Before starting a print, ensure there is no excess plastic hanging from the nozzle tip
- Run the purge sequence and confirm clean extrusion before launching
- If the slicer generates a purge strip, check it is printed away from the print area
- Increase the Z-hop distance slightly in slicer settings so the nozzle clears previously printed material during travel
Probe arm physically bent
Section titled “Probe arm physically bent”Symptoms
Section titled “Symptoms”- Bed mesh is consistently uneven even after Z screw adjustment
- The probe consistently triggers too early on one side of the bed
- Visual inspection shows the probe arm is no longer horizontal
Impact with the bed surface during a failed probe sequence, or aggressive manual handling.
- Gently straighten the arm if it is slightly bent — aluminum arms can be carefully reshaped by hand
- If the bend is severe or at the pivot point: replace the printed probe arm (E21). Do not remove the factory-calibrated metal arm that the printed part mounts to — only swap the printed E21 piece
- After any arm repair or replacement, re-run full bed leveling and re-save the Z offset
After fixing — bed leveling procedure
Section titled “After fixing — bed leveling procedure”- Heat the extruder to printing temperature before running bed leveling (a cold nozzle tip can trigger the probe prematurely)
- From the display: Macros → Bed Leveling
- After the mesh completes, adjust Z screws by hand to flatten the mesh (use Heightmap in G1OS to visualize)
- Save the mesh from the display
- Re-run Z offset and first layer calibration after any probe change
- A redesigned probe arm was introduced in newer machines — if you have persistent issues with the original design, ask Ginger Additive support about the updated part
- Bed leveling must be done with the extruder at print temperature — cold material on the nozzle tip acts as a physical obstruction and causes false probe triggers