Here is the full list of all 15 Bus Mechanic Simulator achievements.
Reach experience level 2.
Reach experience level 3.
Unlock the ratchet.
Unlock the pneumatic screwdriver.
Unlock the light test in the testing bay.
Unlock the brake test in the testing bay.
Unlock the exhaust emissions test in the testing bay.
Use the rubber duck.
Finish your first job.
Finish your first job on a double decker.
Finish your first job on an articulated bus.
Increase your inventory to 60 parts.
Increase your inventory to 80 parts.
Increase your inventory to 100 parts.
Finish the tutorial.