What Will a Car Diagnostic Tell You?

Performing a car diagnostic can reveal a number of problems associated with the transmission, oil tank, gas tank, exhaust system and other components of the vehicle. Modern vehicles designed with computer processors, microchips and sensors can be linked to a car diagnostic computer scan to pinpoint exactly where the problem exists. The scans are performed at a dealership or at the garage of certified mechanic. Some scans can be performed at home using a hand-held scanning device.

In 1996 the EPA mandated that the computer interface of all vehicles sold had to meet the On-Board Diagnostics, version II (OBD II) standard. This meant that aftermarket repair shops would be able to diagnose a problem in the vehicle using only one set of tools and running a simple computer scan. This is now known as the car diagnostic test; the process involves producing a complete report with a set of codes that pertain to different problems.

The car diagnostic can tell you the following about the vehicle:

  • ignition timing issues

  • level of buildup in the combustion engine

  • fuel injector performance

  • whether the ignition coils are firing

  • engine rpm levels

  • air and coolant temperature

  • crankshaft and camshaft position

  • the throttle opening

After the car diagnostic is performed, the computer will tag each data point to reveal what needs to be corrected and stores this code so that the technician can look in a specific area for the problem.

Common Diagnostic Codes
OBD II diagnostic trouble codes can range from P0100 to P1899. Each letter and number in the code represents a different part of the vehicle.

The first letter

  • “P,” which relates to the power train.

  • “B,” it will relate to the body

  • “C” relates to the chassis

  • “U” is undefined

The second placeholder is a generic code shared by all manufacturers and is usually 0, but some manufacturers use a specific code here so the number 1 may appear.

The third placeholder determines the area of the problem.

  • 1 means there is a fuel or air problem

  • 2 means there is something wrong with the injector circuit

  • 3 means there is an ignition problem or the engine is misfiring

  • 4 means there is an emission control problem

  • 5 means there is a vehicle speed or idle control problem

  • 6 means there is a computer or output circuit problem

  • 7 or an 8 means there is a transmission problem.

The fourth and fifth digits of the computer diagnostic check report further identify which system is malfunctioning; the digits that appear here vary by vehicle make, so the mechanic running the test may need to contact the dealership or do some research on what the rest of the code means.