M109 causes second extruder to read false temp


I am currently in the progress of building my second printer, and have encountered an odd problem. This is a SKR 1.3 mobo dual extruder running the latest Marlin 2.0.

Sending a M109 command to either T0 or T1 causes the second extruder to output the maximum possible value set in the Marlin firmware, in this case 260. So if I for instance send M109 S190 T0 to the printer, the T0 starts heating normally, but seconds later T1 returns that the temperature is at 260c.

This is really weird as M104 does not have this effect. I have searched the web and the firmware itself far and wide but have not been able to solve this. A bug, perhaps?

Sincerely, Leevi

Out of curiosity, have you confirmed that the second extruder is hot, or might it just be reporting the max temp?

Hi Stefan!

The printer thinks that the nozzle is above the target temp, whichever it might be, and thus turns the heater completely off. This causes the nozzle to remain cold, so it definitely has something to do with software.

Glad to hear the safety routines are working. If you haven’t reported already (I didn’t find a similar report), this is where you should send the info:


Be as specific as possible, including a copy of your config files (don’t paste them inline!). Considering the size of the team, they respond fairly quickly.