OBD2 trouble codes are part of a troubleshooting system that helps you track down the source of your engine's problems. For example, if the engine's computer recognises a malfunction during operation, it isolates it, translates it into a code and saves it so you can access it. You retrieve it using one of the methods outlined here. Let's say the code indicates a too-rich oxygen-to-fuel ratio. Look this up in a repair manual and you'll see this is usually liked to a faulty oxygen sensor. Replacing it solves the problem and the code resets.
Turn the ignition key "On" and "Off" without cranking the engine. How many times you do this depends on your particular vehicle. Most Chryslers require five times; other cars require three. End with the key in the "On" position. Start the sequence anew if you accidentally crank the car.
Watch the "Check Engine" or "Service" light on the dash. It will be lit, and will begin to pulse. Each pulse represents a number. A pause separates one digit from the next in a two-digit code. For instance, Code 23 will go like this: pulse, pulse, pause, pulse, pulse, pulse.
Write down the codes as they flash through the "Check Engine" light. Each code has a meaning, directly related to a problem in the engine. Look up the codes in a repair manual.
Depress the odometer "Trip" and "Reset" buttons while turning the key "On." Release the buttons and watch the odometer display for the trouble codes to read out digitally.
Depress the odometer "Trip" and "Reset" buttons while simultaneously turning the ignition key "On" and "Off." End with the key in the "On" position. Release the odometer buttons and read the trouble codes from the digital odometer.
Locate the test port under the dash where the OBD2 scanner plugs in. Use a piece of jumper wire or even an unbent paper clip to link ports "A" and "B," initiating the diagnostic sequence. Watch the "Check Engine" light for the codes to flash.
Take your vehicle to an auto parts dealer for a diagnostic check free of charge. Many chain retailers offer this service.