Left lower suspension arm rear bolt broken.

[Lux]

This was a common problem on the older Vitz/Echo (frame code NCP1x series) as well. The problem is that the bolt will corrode and fuse itself with the bushing carrier (specifically: its inner race) that it passes through before treading into the subframe. From my experience, here are your options....

• MIG weld a new head onto the bolt shank and attempt to back it out again. Use heat on the bushing carrier to help.
  
• Use a cutting torch and cut the arm off from the body, then slice the bushing carrier off by making two slits in the shell to expose the rubber bushing (which is probably already on fire at this point). Melt the bushing away to expose the bushing inner race (sleeve). This is where the bolt has seized itself inside. From here, you can either:
  • cut the bushing inner race off along with the bolt shank then blow the entire seized bolt/race out through the subframe and save the threads, or
  • use large Vise-Grips or weld some makeshift lever onto it and to try to back it out.

Both methods will take a tremendous amount of patience and expertise... Good luck!