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Kate on Cars - The Basics of Diagnostics


Kate on Cars - The Basics of Diagnostics

Almost everybody knows that manufacturers are responding to consumer demand and to fuel economy and safety mandates by the federal government by adding more features to the vehicles they make. As automobiles continue to grow in complexity, diagnosing problems with them continues to become more challenging and time-consuming.

What does it mean for a shop to “diagnose” your vehicle? To diagnose something is to identify the nature of it. To correctly diagnose a car problem, the technician needs to identify the nature of the problem. Techs need correct and adequate knowledge to do this, and they need to have adequate tools as well.

The diagnostic process is just as important and necessary as the repair process. Therefore shops need to charge money for this, and technicians need to be paid for their expertise, their knowledge, and their tools.

And guess what – it often takes time to generate an accurate diagnosis.

The process of diagnosis starts with gathering information. What are the symptoms of the problem? When and how often to they occur? Are there any codes in any of the vehicle’s computers (in fact - some modern vehicles have 250 or more computers in them)? What system are the codes pointing to? What does a visual inspection of the vehicle and system reveal?

What do specific tests of these systems and components reveal? Each time it is a beautiful process of discovery – at least in my opinion.

Even the best technicians are not going to be 100% right about what’s wrong with a vehicle 100% of the time. There are just too many variable to consider. Sometimes one problem masks another problem, and sometimes repairs need to be done one layer at a time to get to the bottom of the issue. So it’s ok to cut your shop a little slack on this.

Shops charge for diagnostics because it takes a great deal of technical experience and often very expensive tools in order to perform one. A technician doesn’t just plug the (very expensive) scan tool into the car and have the scan tool tell the tech what the problem is. If you’ve heard that, it is incorrect. The computer(s) on your automobile are programmed to note when something is amiss. They can make suggestions about where the problem is, and what sensor or component might possibly be the cause of it, but computers do not tell technicians definitively what the cause of a symptom is.

So what if you think you know what is wrong with your car? Should you tell the shop to replace what you think is the bad part? Well, you can. But a thorough shop will explain to you that certain testing needs to be done first to locate and confirm a faulty part. A good shop will put your safety first. Proper diagnostics are the first step towards achieving a correct repair that will help keep you and your family driving safely.

It’s like going to the doctor. If you’re sick, your doctor will ask you a bunch of questions about your symptoms. But then they do a bunch of tests too to determine what is making you sick. If you’re really sick or if the basic tests don’t confirm what’s wrong with you, your doctor doesn’t usually say “ok, let’s just treat you for this then,” without knowing what you have. No, they go back and do more tests until they figure out what is wrong. This can take time. It’s the same thing with auto repair.

So get regular checkups with your doctor and grant your automobile the same good treatment. And hopefully now you’ll understand a little better why your repair shop aka “car doctor” needs to do the testing that it takes to correctly diagnose and repair your auto.

If you have any questions or thoughts about diagnostics or auto repair in general, email me at