HMS 1A00-3000-0001-0040: Hotend Presence Detection Sensor Is Open-Circuit
LayerWalker is a participant in the Amazon Services LLC Associates Program. We may earn a commission when you buy through links on our site, at no extra cost to you.
HMS 1A00-3000-0001-0040 means the toolhead sensor that detects whether a hotend is present has gone open-circuit, and Bambu gives you both options in order: reconnect the sensor cable, or replace the sensor. Open-circuit means no connection at all, which is why a cable is the first suspect.
This is a wiring fault with a name attached, which makes it one of the more tractable codes in the group.
Where to buy
Open-circuit points at the cable
A failed sensor usually reads wrong rather than reading nothing. A complete break is more often a connector that has worked loose, and the toolhead is the most mobile part of the machine, so its connectors see the most movement. Power down, unseat the connector, and reseat it until it clicks. The platform and where its cabling runs are covered in the Bambu Lab H2D.
Then look along the run
Follow the cable through its travel and look for a pinch point, a chafed spot where it rubs, or a kink where it has been routed tightly after a previous repair. A conductor broken inside intact insulation reads exactly like a disconnected plug and is easy to miss.
Confirm with a meter before buying
Continuity across the sensor circuit tells you whether the break is in the cable or in the sensor itself, and that is a two-minute test that decides which part to order. The same approach applies to other sensing faults on these machines — see 3D printer thermistors for the general method.
What HMS 1A00-3000-0001-0040 explains
Without presence detection the machine cannot tell a loaded slot from an empty one, which is why this often arrives alongside HMS 1A00-0100-0002-0003. A hotend you can see reported as missing is the signature of the sensor rather than the slot, and treating it as a handling problem wastes the afternoon.
Printing while it is open
Tool swapping depends on this sensor, so swapping is out until it is fixed. What the equivalent sensing does elsewhere on a printer is covered in bed levelling sensors.
HMS 1A00-3000-0001-0040 FAQ
Is open-circuit worse than short-circuit?
Not worse, just different. Open means no connection; short means an unintended one. Both have their own code.
Can I bypass the sensor?
No, and you would not want to. It is what stops the rack placing a hotend into an occupied mount.
Did a nozzle change cause it?
Often, because the connector is disturbed during that job. Reseat it first.
Which part do I order?
Whichever the continuity test implicates. Guessing here costs you a part you did not need.
Not every detection problem is electrical. HMS 1A00-0100-0002-0033 means the hotend never seated properly, and the two surfaces Bambu names are both cleaning jobs.
LayerWalker
Print defect diagnosis, calibration procedures and parts that actually fit. Corrections welcome through the contact page.
