Performing diagnostic tests on a vehicle depends on the year of manufacture. Vehicles after 1996 operate under the second generation of On-Board Diagnostic coding. Also, if your car or light truck is manufactured after 2008, it will likely have a tire pressure monitoring system. There are other self-monitoring systems in the brakes and in airbags. All of these systems can be accessed with a scanner through the diagnostic outlet usually on the driver's side of the vehicle. If your vehicle predates 1996, diagnostic procedures vary by make and model. You will have to consult your manual and resources specific to your vehicle.

Instructions
1 Visit an automotive retailer and shop for a code scanner. The more you pay, the more features the scanner will have. Some higher end diagnostic tools are multilingual or can diagnose more than one system. Cheaper tools are dedicated only to OBD-II codes. Also, the scanner you chose to buy will also depend on which trouble indicator light is active on your vehicle. You will have a regular "Check Engine" light, as well as a separate light for brakes, airbags, and tires. If your airbag light is active, you should drive your car to a mechanic; diagnostic tools are not as widely available, and the needed repairs are more complex.

2 Hook the diagnostic scanner to the computer outlet on the driver's side of the car. For most cars, this outlet is under the dash, somewhere between the gas pedal on the right and the hood release on the left. It is often black in color, and will feature 16 pin receptors. The plug at the end of the scanner's cable should easily fit, so do not jam it in. If you cannot locate this outlet, there are websites like CarMD.com that will tell you where it is.

3 Turn the scanner on. You will have to do this for some diagnostic tools, but not for others. Some scanners will turn themselves on once a link with a vehicle's diagnostic system is sensed. The process might differ slightly by brand and diagnostic system, but the process is basically the same

4 Insert your key into the vehicle's ignition and turn to the "On" or "Run" position. This also may vary according to vehicle type, so consult your manual.

5 Wait a few seconds while the diagnostic system and the scanner establish a connection. You will know the two systems are linked once a trouble code appears on your scanner.

things you'll need:Diagnostic code scanner