Fix Bambu P2S start gcode: M975 before M982.2, remove redundant G28 post-leveling #35

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MrUnknownDE · 2026-04-05T16:18:13+02:00

MrUnknownDE commented

2026-04-05 16:18:13 +02:00

Originally created by @scoofz on 4/1/2026

Summary

Fixes two bugs in the Bambu Lab P2S machine start g-code. Closes #11741 (P2S profile is outdated).

Bug 1 — Motor noise reduction activated before input shaping is enabled

The stock sequence calls M982.2 S1 (cog noise reduction) before M975 S1 (input shaping) in the machine reset section:

M983.1 M1
M982.2 S1   ; ← noise reduction, but input shaping isn't active yet
M983.4 S0

M982.2 depends on M975 being active to have any effect. In the stock code, M975 S1 is only called much later (after the mechanical sweep), so noise reduction does nothing during the noisiest part of the startup sequence.

Fix: M975 S1 is moved immediately before M982.2 S1 in the reset block.

Bug 2 — Unconditional full XYZ rehome after every bed leveling

In the stock sequence, a bare G28 sits unconditionally right after the bed leveling block, outside any conditional (M622/M623) guard:

M622 J0
  G28       ; correct: homing only when ABL is skipped
M623
G29.2 S1
G28         ; BUG: runs unconditionally, every single print

This causes a full XYZ rehome after every print startup regardless of whether bed leveling ran or not — in addition to the initial homing already performed earlier in the sequence.

Fix: The unconditional G28 is removed. The G28 inside the M622 J0 block (no-ABL path) is left intact.

Files changed

resources/profiles/BBL/machine/Bambu Lab P2S 0.4 nozzle.json — the 0.2, 0.6, and 0.8 nozzle variants inherit their machine_start_gcode from this file

Testing

Both fixes have been tested on a physical P2S with AMS 2 Pro. Community feedback on Reddit (r/BambuLab) and the Bambu Lab forum has confirmed the noise reduction fix produces an immediately audible improvement in startup behavior.

Reference: https://github.com/scoofz/P2S-start-gcode

*Originally created by @scoofz on 4/1/2026* ## Summary Fixes two bugs in the Bambu Lab P2S machine start g-code. Closes #11741 (P2S profile is outdated). --- ### Bug 1 — Motor noise reduction activated before input shaping is enabled The stock sequence calls `M982.2 S1` (cog noise reduction) **before** `M975 S1` (input shaping) in the machine reset section: ```gcode M983.1 M1 M982.2 S1 ; ← noise reduction, but input shaping isn't active yet M983.4 S0 ``` `M982.2` depends on `M975` being active to have any effect. In the stock code, `M975 S1` is only called much later (after the mechanical sweep), so noise reduction does nothing during the noisiest part of the startup sequence. **Fix:** `M975 S1` is moved immediately before `M982.2 S1` in the reset block. --- ### Bug 2 — Unconditional full XYZ rehome after every bed leveling In the stock sequence, a bare `G28` sits **unconditionally** right after the bed leveling block, outside any conditional (`M622`/`M623`) guard: ```gcode M622 J0 G28 ; correct: homing only when ABL is skipped M623 G29.2 S1 G28 ; BUG: runs unconditionally, every single print ``` This causes a full XYZ rehome after **every** print startup regardless of whether bed leveling ran or not — in addition to the initial homing already performed earlier in the sequence. **Fix:** The unconditional `G28` is removed. The `G28` inside the `M622 J0` block (no-ABL path) is left intact. --- ### Files changed - `resources/profiles/BBL/machine/Bambu Lab P2S 0.4 nozzle.json` — the 0.2, 0.6, and 0.8 nozzle variants inherit their `machine_start_gcode` from this file ### Testing Both fixes have been tested on a physical P2S with AMS 2 Pro. Community feedback on Reddit (r/BambuLab) and the Bambu Lab forum has confirmed the noise reduction fix produces an immediately audible improvement in startup behavior. Reference: https://github.com/scoofz/P2S-start-gcode

MrUnknownDE added the bug-fix bug-fix profile bug-fix profile labels 2026-04-05 16:18:13 +02:00

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Reference: github/OrcaSlicer#35