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What Is a Car Diagnostic?

Since 1996, all new vehicles have been equipped with technology to aid in car diagnostics.
Mechanics can test a vehicle's battery as part of a car diagnostic.
The codes refer to parts of the car, such as P for powertrain.
Mechanics can explain to customers what the car diagnostic codes mean, and how they should be repaired.
A car diagnostic pinpoints a car's problem, making a mechanic's job substantially easier.
A transmission issue often reads as a location 7 or 8 during a car diagnostic.
Article Details
  • Written By: M.R. Anglin
  • Edited By: Jenn Walker
  • Last Modified Date: 15 September 2014
  • Copyright Protected:
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    Conjecture Corporation
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When a person buys a car, he usually expects it to run well for a long time. To this end, car manufacturers have developed sophisticated computer systems that keep the car in check and help to keep it running smoothly. Those systems will also light up the check engine light when there is something wrong with the car. A car diagnostic is a test that tells a person what is causing the check engine light to turn on. Once the problem is identified using this system, the mechanic can go forward in fixing it.

Many cars now have a computer system that keeps it in check. This computer system is constantly receiving information from the different sensors in the engine and adjusting those systems so the car can run smoothly. It is this computer system that also controls the check engine light. When there is a problem the computer cannot fix itself, it triggers the light so a mechanic can identify and solve the problem. The system also produces a code that can be used to help identify the area and nature of the problem.

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In order to make the process of running a car diagnostic easier, many cars have an On Board Diagnostics, version II (OBDII) computer interface. This interface allows for a mechanic to use one tool to identify problems on virtually all makes and models of cars. To run the test, a scanner is inserted into the connector, usually located under the driver's side dash. After some information about the car's model, vehicle identification number (VIN), and engine type is entered into the scanner, it can identify and capture the diagnostic code. It is this code that helps the mechanic to know where to look to find the problem.

An example of a car diagnostic code is P0131. Each section of this code refers to something specific. The first section of the code is a letter that refers to a general area. P refers to powertrain, B to body, C to chassis, and U to unidentified. The next section, a number, is the manufacturer's code. Often, this is a generalized 0, but some times it may be a 1. The next number to appear refers to the area of the problem. Each number from one to eight refers to a different area. For example, a 1 refers to an air or fuel problem, a 2 to for an injector circuit problem, and a 7 or 8 to a transmission problem. The last two numbers in the code more specifically show where in the localized area the problem lies. These numbers may vary by car manufacturer, so the mechanic may have to call the manufacturer to identify the exact location.

A car diagnostic can make finding an automotive problem much easier. Instead of having a mechanic give the entire engine a check, a machine can do it for him. In addition, some diagnostic scanners are available for consumers to purchase. With one in hand, a consumer can have more knowledge on what is going on in his car. A consumer scanner can also store codes for problems that may not show up when the car is taken to the mechanic.

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