Auto Leveling Crashes Print Head at Third Sample Spot

When doing a nine point auto leveling at the start of a print the print head crashes into the bed after successfully sampling the first two spots. I use Repetier firmware and host on a Tronxy P802MA. 

I'm using G28; home all axes (works fine)
Followed by G29; auto level (samples first 2 of 9 spots fine, then drives head into bed at third spot until I hit emergency stop.)

This started after I tried printing from an sd card for the first time (unsuccessfully). I've had no problems printing via usb up to now. I don't need to use the sd card, so I'm trying to get back to using the usb as I did before. 

This seems like a software problem. Any suggestions? 


  • I solved the problem on my own by sending the following to correct the corrupted eeprom:
    M502 ; Load values from configuration.h
    M500 ; store values to eeprom
    Hope this helps someone else.
  • G29 is a marlin code for bed levelling.
    Repetier firmware uses G32 for bed levelling or G33 for mesh levelling

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