As a customer with an uncommon vehicle issue, you may find it is best not to speculate on the issue, and simply tell the technician "fix it". Any information you can provide the technician is helpful, and the technician will go into diagnosing an unknown issue, also known as general diagnostics.

When a vehicle comes in for repair, and there is an obvious fault, such as "the wheel bearing is grinding or the brakes squeal at stop lights", these problems are generally not diagnosed, as the technician already understands the problem after inspecting the vehicle. Problems such as, "I hear a thump sometimes" or "my car feels like I'm in an airplane", are more vague, and until the technician knows what system is at fault, or verifies the existence of a fault, the process used is general diagnostics. With general diagnostic procedures, the servicing will systematically move through the systems of a vehicle until the fault is uncovered.

Like we noted in the last section, general diagnosis symptoms are the most vague of the bunch. There are several diagnostic spectrums, electrical diagnosis, drivability diagnostics, engine diagnostics, transmission diagnostics, and the list could continue for about 5 or 10 more spectrums of diagnostics. The most important take-away here, is that general diagnostics are diagnostics that have no other spectrum in which they fit, or the problem is unknown. This means that any vehicle left outside of a repair facility with the keys and an authorization to perform diagnosis will be diagnosed under the general diagnosis spectrum.

As far as general diagnostics go, the answer is maybe. If it is uncertain if a vehicle is safe to drive, take the safe route and have it towed. If the issue is just a random noise, or the check engine light pops up, driving the vehicle is normally not an issue. However, if the vehicle is unsafe to drive, difficult to keep under control, or responds poorly to driver input, the vehicle should be sent to a professional technician.

Vehicles are under general diagnosis every time they have an inspection performed. When a technician takes a vehicle on a road test, and does a complete visual inspection, the technician is, much like general diagnosis, systematically checking the fitness of each system in the vehicle. However, thousands of vehicles with a wide array of issues undergo general diagnosis every day, and their age and mileage can be vastly different.

When a vehicle must be diagnosed, the technician will establish a diagnostic strategy based on the observed symptoms. There are a few general starting points which are assigned according to what the vehicle will, or will not do. For instance, a vehicle that will start, but the engine immediately stalls is called a "start and stall" issue, and a specific diagnostic process is used to identify the cause of the condition. It is important to keep in mind that general diagnostics will lead to another form of diagnostics once the issue is able to be categorized according to the system that is causing the failure.

Corrections for general diagnostics issues usually involves replacing simple components, such as the battery, alternator, a blown fuse, or a bad coil. However, due to the wide variety of components that can possibly cause a problematic condition, repairing this issue could involve replacing a fuse, or replacing the engine, and repair procedures are on a case-by-case basis.

Diagnostics in general can be problematic, and there are many variables to account for when the issue, or the cause of this issue is unknown. When problems arise, diagnostics may take several hours to complete, or just a few minutes. This will significantly impact the cost of repairs. Choosing a facility with proper equipment and training for their staff may significantly reduce diagnostic time needed.

Diagnosing modern automotive systems without proper knowledge and training can be frustratingly difficult, but without proper technique the diagnosis will only be reached through changing parts on a hunch. Automotive systems, especially in the last several years, have become extremely advanced, and most vehicles have a communication network that allows all of the systems to communicate. This is a blessing for the trained technician, and a curse for the DIYer who would rather save money on the repair.

General diagnosis should be attempted by the experienced DIYer, with a good understanding of all affected vehicle systems, and the proper tools and techniques to diagnose a variety of issues. The task of diagnostics should be left to a professional technician once all knowledge and tooling resources are dissolved, as damage may occur without excellent knowledge, skill, and tooling.