The on-board diagnostic system known as “OBD” made its debut in the 2000s, and is now part of most vehicles manufactured since then. This tool allows you to get a more precise reading on diagnostic trouble codes and is connected via a plug known as the “OBD (On-Board Diagnostic) plug”.
This system helps detect diagnostic trouble codes thanks to sensors that inform the on-board computer. These diagnostic trouble codes are communicated to the driver of the vehicle via an indicator light on the dashboard called an MIL (Malfunction Indicator Lamp).
In order to understand these diagnostic trouble codes and translate them into human language, we use a diagnostic kit, an IT tool that stores all the possible diagnostic trouble codes that can come up in a vehicle, based on its features, year of manufacture, motorization and various technologies the vehicle uses.
Knowing how to decipher a diagnostic trouble code
The first letter indicates the diagnostic trouble code family:
P: Powertrain group, in other words, the engine and the transmission
The first number indicates whether or not the code is generic (green digit):
The last three numbers correspond to the following:
0, 1 and 2: Fuel and air metering
3 : ignition system
4 : auxiliary emission control
5 : vehicle speed and idle
Source : http://www.outilsobdfacile.fr/