The most obvious sign your exhaust is failing is noise. If your car is louder than usual or you hear loud ticking, tapping, thumping or droning sounds then you may have broken or lose components. You may also smell exhaust if your system has a hole or leak in it.
Smell of exhaust inside the vehicle, holes or rust in on the exhaust system itself, low air vaccume pressure, and irratic readings of air flow. Also possible backfiring, large consumption of gas, and gauge malfunction.
Well the most obvious would be how loud it is. Most newer vehicles have sensors that will turn on your check engine light. But other things to look for are backfiring and a fouled ignition rotor,trouble starting the vehicle. Your engine has to breathe in and OUT so if your exhaust is plugged it probably won't even start
Several actually - car seems to be excessively loud when running, smell of exhaust inside the vehicle, poor performance on the road, worst case would be engine fire due to manifold issues
Exhaust noise always means trouble. But even if you can't hear anything, it may be leaking. Any time you are under your vehicle to change oil or do other repairs, you should take a few minutes to inspect the exhaust system. original equipment exhaust systems typically go about five to seven years before mufflers and pipes start to rot.