Here are the explanations of the make up of a diagnostic fault code Prefix:
| First (Character) | Identifies the Related System |
| P | Powertrain |
| B | Body |
| C | Chassis |
| U | Network |
| Second (Digit) | Type of Code |
| 0 | Complies with EOBD Standard |
| 1 | Manufacturer Specific Enhanced |
| Third (Digit) | Sub-System Affected |
| 0 | Fuel and air metering and auxiliary emission controls |
| 1 | Fuel & Air Metering |
| 2 | Fuel & Air Metering Injector Circuit |
| 3 | Ignition System or Misfire |
| 4 | Auxilliary Emission Controls |
| 5 | Vehicle Speed & Idle Control Systems |
| 6 | Computer Output Circuit |
| 7 | Transmission |
| 8 | Transmission |
| Fourth & Fifth (Digits) | These refer to the specific fault within the sub-system |