Job Progression
Jobs - Car Mechanic Simulator 2015
Once you start to gain a bit more experience in Car Mechanic Simulator 2015, the job complexity will start to increase. After a while the parts lists will either be only partially complete or not present at all. Everything will just say 'part not discovered'. Welcome to the diagnostics part of the game.
Also, keep a close watch on any jobs involving the body. Why? They will quickly start to include 'Paint Car the Factory Color', and if you don't have the Paint Shop you will not be able to get full completion on the job.
On the up side, as jobs get more challenging they tend to get far more profitable. So at this point you should be able to buy a few of the diagnostic upgrades.