What are Fault Codes? With modern vehicles relying on electronic systems for almost every aspect of operation, from throttle control to adjusting your seat position, everything is managed from a central computer, known as the Electronic Control Unit, or ECU. While these systems do a great job in keeping a vehicle operating smoothly and as efficiently as possible, unlike older vehicles where mechanical issues are more obvious, if things go wrong in your electronic systems, it can be very difficult to know where the problem lies. The solution to that is the fault code, sometimes called diagnostic trouble codes (DTCs), which are generated by the ECU when it detects a problem anywhere in the vehicle. Each code is unique, and relates to a specific vehicle system, or component within a system, dramatically speeding up the diagnostic process for technicians. What is a Pending Fault Code? This refers to fault codes that are stored within your vehicle’s onboard computer. Pending fault codes alert you or the maintenance technician that the control system has detected a potential problem, but that the problem has not yet been confirmed through repeat occurrences. Because they are not fully confirmed as a repeating fault, pending fault codes are a way to monitor intermittent problems, and can be thought of as an early warning system for issues that may be developing in the vehicle. If the fault repeats over multiple drives, the ECU can elevate the issue to a confirmed or permanent fault code, signifying that immediate attention is required. What is a Permanent Fault Code? Also stored in the vehicle’s ECU, the permanent fault codes are a type of DTC that identify a conformed issue with one or more vehicle systems. These permanent codes cannot be cleared by disconnecting the battery or by using a scan tool, as other fault codes can, because they represent a significant issue that needs immediate attention. Instead, they only go away once the ECU itself determines the problem has been fixed. This usually takes a few drives in the vehicle without the issue appearing. Permanent fault codes are crucial in identifying issues that consistently affect a vehicle's performance or emissions. Fault Codes — Your Vehicle’s SOS Signal Fault codes are your vehicle’s version of an SOS signal, telling you that something is wrong and help is needed to fix it — this is also known as the check engine light. Whether they are being read by a dedicated code reader, a scanner tool or a telematics unit fitted to your vehicle, these codes are generated by the ECU to help identify what the problem is and where it is located. From an issue with the ABS system to an engine misfire or anything else, these unique codes point the way to dealing with the issue. Fault Code Definition With a unique code for every issue, reading fault codes can seem like looking at a secret language, but there is a logic behind them that makes it easier than it first appears. Each code starts with one of four letters: P — Powertrain B — Body C — Chassis U — Undefined This is then followed by a 4-digit number, and together they tell you where an issue can be found. For instance, the code P0300 indicates an engine misfire has been detected. This allows your technician to begin their investigation where the problem actually is, making it faster to solve the issue. Conclusion Fault codes are a way for the ECU in your vehicle to tell you what is wrong, so that it can be fixed faster and more efficiently. If you understand these codes, you can spot issues early and this can keep you safer on the road, but it can also save you money, ensuring you fix issues before they become larger problems.