- Troubleshooting automotive computer circuits has become a bit easier over the years with the advent of some of the more advanced diagnostic tools, but the mechanic must still know what each circuit does and how it affects the car. The computer will tell you which sensor is bad, but the mechanic must remember that when working with a car's computer system and sensors, each problem will always affect something else.
- The advanced scanners are quite expensive and only large shops have them, but a small scanner can be purchased at any big box automotive store. This small scanner can help a small mechanic or a backyard mechanic with diagnosing problems with the computer circuits. Plug the scanner into the port underneath the driver's side dash. Turn the key on and push the "Read" button. The scanner will read the codes. Match the codes to the code sheet that comes with the scanner.
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If the engine light is not on, in most cases you won't be able to pull a code. The engine light only comes on when one of the sensors isn't working properly. If you see the engine light come on and go off by itself, in most cases, this is the oxygen sensor. The oxygen sensor senses the fuel/air ratio. Just because you get an oxygen sensor code, it doesn't mean the oxygen sensor is bad. This is a classic example of one component affecting another component. If you get an oxygen sensor code, you should always check the plugs and wires (if applicable), the distributor cap and rotor (if applicable). There are other things that can affect the air/fuel ratio, but the ignition components are usually suspect.
Another example of one sensor affecting another is the MAP sensor and the EGR valve. Both can cause the car to send black smoke out of the exhaust. Sometimes you may get a MAP sensor code, but the EGR valve is the sensor causing the problem. Before buying the MAP sensor (if that was the code you got), be sure the EGR isn't sticking. -
If you get "weird" codes--codes that do not exist--in most cases, the computer is suspect. The computer can't diagnose itself, so it will send erroneous information to the code scanner. If the computer is bad, it will generally send information to the scanner that doesn't exist. The codes won't be listed on the code sheet.
Sometimes the computer will send more codes than what is wrong with the car. If you see too many codes but know that five different sensors can't be bad, the computer is also suspect. When you see this, you can take a chance and replace the computer or you can take the car to the dealer or a trusted professional mechanic to double-check your diagnosis. If the computer isn't expensive, you can try to replace it yourself--but if you have an expensive computer, it's better to have a professional check it. - There are many things that can go wrong with automotive computer circuits. Always check with a professional mechanic if you're unsure about replacing parts. Paying someone to diagnose the computer and sensors when you aren't sure what the problem is can save you money, as many of the sensors and the computer aren't returnable. When working with the computer, even static electricity can burn a circuit--so always use caution when working with the computer.
