There are a handful of upgrades and tools available in Car Mechanic Simulator 2015. At first they are slow to unlock, but what do they do, and in which order should you get them? This guide will help you answer those questions.
General tools mainly improve the speed at which you can perform various actions, though it does contain one exceptional item: the Tablet. This is the perhaps the very first item you should get, as far as upgrades go.
I find the least useful item out of all the tools is Fast Manual Examination. I almost never use it; I almost never need to. Most defects you'll either find by looking or by using other tests. This one should probably be the last choice.
Fast Unbolting & Fast Assembly/Disassembly are helpful, but before getting these items I would definitely recommend looking into the Examine Tools category. These tools will be very helpful to you in enabling you to pinpoint many problems.