Diagnosing Car Problems

By Brian Klaubert

How many people have you heard say, “I used to be able to fix about anything on my car, but not anymore”? Undoubtedly cars have become more complex, but they have also become more reliable, longer lasting, and have greater creature comforts. Think back 10 or 15 years ago. Nobody wanted to go 100,000 miles on their car before getting rid of it. Now it is very common to have a 4-6 year old car with 150,000 miles on it.

However, when a problem does occur, diagnosing the root problem has become more complex. Most vehicles today have 4 to 7, or more, computers. Those computers communicate constantly over a network. Yes, just like in the office, all of your vehicle’s computers are networked together. Frequently the customer reported problem is a symptom of a root cause problem somewhere else.

Would you believe that when you turn on your headlights, windshield wipers, rear defroster, air conditioner or most other accessories, the switch you move is only talking to a computer. The computer then turns on the accessory that you intended to control. In fact, it is becoming more and more common that your gas pedal is not even connected to anything other than a computer. Step on the gas, and the computer moves everything needed to make the engine run faster. This is called “fly by wire”.

Diagnosing problems requires more knowledge and experience than it used to. A technician must know how systems integrate together and how to track problems from one system back into another.

Unfortunately, and contrary to widely held public belief, there is no “magic oracle” diagnostic tool or computer. You cannot just plug a vehicle into the “magic oracle” and have it spit out everything that is wrong with a vehicle.

Additionally, if the car is not exhibiting the symptom when it is diagnosed, the computer cannot report a problem. This would be analogous to going to the doctor, reporting that you had a fever last week, and asking that he specifically identify exactly what caused it. If he looked at you when you had the fever, he would have something to work with, but not if the fever is not present.

The diagnostic computer plugged into the vehicle provides access to raw data running to and from the computer. It also provides access to trouble codes that the vehicle computer has recorded when self diagnostic tests have observed a problem. The trouble code frequently does not report the defective part or system, just the defective symptom.

To take a simpler example, EGR faults are frequently quickly diagnosed as requiring a new EGR valve. Actually, the EGR valve itself is the most robust part of that system. More frequently the ports before or after the valve are clogged or the independent sensor that evaluates if the valve is doing its job has failed. But since any of those three can cause the problem, all three must be checked out.

Lastly, the overall condition of the vehicle plays a big role in how quickly the root cause of a problem can be found. If the vehicle has had little or no maintenance done, problems and symptoms can mask or multiply. You may have to correct some glaring problems first, only to learn that a more subtle problem is also present.

Brian Klaubert own Christian Brothers Automotive – Hamilton Mill on Hwy 124 in Dacula. (770) 271-4080.