The exhaust system is the easiest system to diagnose and repair in Car Mechanic Simulator 2015. Most of the parts cannot be repaired and must be replaced. In addition, they can all be inspected simply by looking at them, which makes things much easier.
A visual inspection is all it should take to find the faults. Look under the hood first to inspect the exhaust manifold(s), and if present, the turbo and exhaust manifold cover.
After that you can put the car up on the lift and inspect the rest of the exhaust system. Do keep in mind that there are only a few parts that have any chance of being repaired. The Exhaust Manifold, Exhaust Manifold Cover, and possibly the Turbo can be repaired. Also keep in mind that if any part is too badly damaged it simply cannot be repaired.
All other parts of the exhaust system are good for the garbage and must be replaced with new parts.
The only vehicle that is a bit odd compared to the rest is the Maluch. Its entire exhaust system is accessed from under the hood. Remember, that the Maluch is rather backwards and the hood and engine are in the back.
While the OBD Reader can diagnose the Catalytic Converter (on cars equipped with the OBD & Catalytic Converter), it is a waste of time unless you are using it to diagnose other problems with the vehicle.
Parts that must be replaced include the Front Exhaust Pipe, Middle Muffler, Rear Muffler, Exhaust Pipe, Catalytic Converter.
To help you learn the diagnostics side of Car Mechanic Simulator 2015 as quickly and easily as possible, I have created a few short but comprehensive guides covering each problem category. For a complete listing of these guides, check here:
Diagnostics & Repairs - Car Mechanic Simulator 2015
If you are looking to learn about the early and mid-stages of the game, you may find these pages of interest:
Your Garage, Tools, Tests, & Upgrades, Jobs & Job Management
And if you are wonding what awaits beyond and where the real cash is hiding, check out this link:
Rebuilding Guide - Car Mechanic Simulator 2015