There’s no such thing as a “no warning” car problem. However, the symptoms are very difficult for a novice to diagnose, and can be very misleading. While many people are intimidated by the physical aspect of fixing a car (i.e. actually tightening a bolt), the real problem for a new mechanic is knowing where to start. While swapping parts at random may seem like a good way to tackle the problem, it very rarely is. Instead, most car problems will give you a symptom, which can be used to identify a system which probably contains the problem. For example, a noise when you use the brakes likely indicates a problem with the brakes. A vibration at low engine speeds likely indicates a problem with either air intake or fueling the engine. A long crank time likely indicates a problem with either the battery or starter motor. Knowing which system to suspect, based on the observed symptoms, is the first trick to fixing cars.
Before you do anything, observe the car. Note when the problem happens, look for odors, check the instrument cluster, and observe whether anything has changed. Do this simple drill: start the car, let it run for a minute, then press the gas lightly while in neutral/park. See if you feel anything, hear anything, or if it hesitates. This drill helps you notice things and establishes a “norm” in your mind. If you don’t have a “norm,” you won’t recognize a problem, even if it’s obvious. Take notes in a notebook or on your phone. Writing things down helps you refine your thoughts and keeps them from getting lost.
We can sometimes fall into the trap of thinking that the most obviously visible issue is the main cause for the problem. Say for example that there is smoke coming out from the bonnet; the car could well be in danger of falling apart, but more than likely the smoke is just the result of a leak of oil hitting a hot engine component. This is an easily identifiable symptom for the novice to get distracted by, where as it is more important to think about the possible causes, trace backwards from the symptom to what could be causing it. You would be surprised how often it pays off to pop the bonnet and have a quick look for loose connections, or leaks in the correct circuitry.
When you have a car that you can practice on, do so. It takes only 15 minutes to pop the hood on your car in your driveway and take a good look around, every day. If nothing else, just check the fluids, look for belt cracks and follow the cables and wires with your eyes. That way, when something is wrong, it’s easy to see. If you have access to several cars, you can get some practice in, especially if the cars are all different. You’re not looking to fix anything at this point, you just want to be able to identify things.
A lot of this work can be detected in its absence. You’ll know you’ve made strides when you stop second-guessing yourself and wandering aimlessly, and when you start navigating the engine compartment in a methodical way from one system to the next. It’s here, where curiosity replaces uncertainty, that you actually start to build your mechanical abilities — not while removing and replacing major components.