A trouble code is an alphanumeric value that corresponds to a particular type of fault. Such as a PO300. The list was originally created by the Society of Automotive Engineers (SAE) for use by all vehicle manufacturers who must comply with on board diagnostic (OBD II) emissions regulations in the U.S.
The list of trouble codes is subdivided into four basic categories:
Powertrain (“P”) codes (engine, some transmission and most emissions systems)
Body (“B”) codes (Climate control system, lighting, airbags, etc.)
Chassis (“C”) codes (antilock brake system, electronic suspension and steering systems)
Network Communications (U”) codes (controller area network wiring bus and modules) Self braking, lane change and other more sophisticated systems.
Most handheld code readers only read “P” codes which is limiting. This means, of course, that there could be other system failures that only a factory type scanner can read.
Many believe a plug code reader, like at some parts stores, retrieves the code, for example a PO301(misfire on cylinder #1) and replace parts. The cause might be a spark plug, a wire, a fuel injector, an air leak or even a rat chewed a wire harness (more common that you think). What parts would you replace?
Yes, it’s tempting to replace the parts yourself and if you have the know-how, go for it. I always recommend you let a professional do the testing and repairs in order to save replacing unnecessary parts.
Keep in mind that the last item in the new systems have resets when some parts are replaced. A code reader will not reset these systems.
Enjoy your car and remember, few things in this world are free.