DTCs, commonly referred to as “fault codes,” play a crucial role in modern automotive diagnostics. These alphanumeric codes are generated by onboard diagnostic (OBD) systems to indicate potential problems within the various control units that equip a vehicle. Understanding these codes is essential both for the technician working on the vehicle and for the person responsible for the file, as they provide valuable information about the vehicle's health and help identify underlying issues.
These codes typically consist of a letter followed by four digits (e.g., P0420). Each code corresponds to a specific problem or malfunction, making it easier to identify and resolve issues during diagnostic procedures.
There are two types of DTCs:
Generic DTCs
These are codes that, as their name implies, provide generic faults that do not always offer specific details for each vehicle model.
Manufacturer-Specific DTCs
In addition to generic codes, automotive manufacturers can also implement their own proprietary DTCs to provide more specific information tailored to their systems and components. These codes can offer deeper insights into the root cause of a problem, making diagnostics and repairs more effective.
Error codes must comply with the OBD standard, and here’s how to interpret them.
The first letter indicates the fault code family:
P (Powertrain): Refers to the powertrain, meaning the engine or transmission.
C (Chassis): Refers to parts outside the passenger compartment, such as brakes, steering, or suspension.
B (Body): Refers to parts within the vehicle's passenger compartment.
U: Fault codes starting with "U" are generally associated with communication problems between the various electronic modules of the vehicle. These codes often indicate issues with the network, connectivity, or communication between the control units and the different vehicle systems.
The first digit following the letter indicates whether the fault code is generic or not.
0: Generic fault
1: Manufacturer-specific fault
The last three digits correspond to:
0, 1, and 2: For air/fuel mixture control
3: Ignition system
4: Auxiliary emissions control
5: Engine idle control
6: Actuators, sensors, or control devices sending information to the relevant ECU
7-8: Transmission
In the field of engine tuning, it is imperative to perform a vehicle diagnostic before an intervention to detect any possible anomaly on the vehicle and also after file writing, as a flash can leave faults that were not erased by the interface used for reading and writing the file.
Having an efficient multi-brand diagnostic tool is indispensable and will allow for much more precise work.
OLSx offers an option called DTC OFF. This option allows for the removal of a fault present in the engine control unit (P fault). Note that this option allows for the removal of a fault and thus a potential engine light on the dashboard, but it does not in any way fix a mechanical issue. We recommend using this option if mechanically everything is in order on the vehicle but, despite all changes, the light and the faults keep reappearing. It will not be possible to fix a problem via a DTC OFF on a vehicle that goes into safe mode with a recurring fault, for example. In such a case, the issue needs to be resolved mechanically first.
There are several types of DTCs:
- Standard DTCs: These are only there to warn of an anomaly but have no effect on engine management (e.g., safe mode). These DTCs can generally be deleted without consequences (note that this does not mean the potential failure disappears).
- DTCs related to functions or monitoring: These are known as “major” faults, related to significant failures (ignition, turbo, richness), and you cannot delete them as they will cause other cascading faults and new associated failures.
The DTC removal tool offered by OLSx should be used with caution; we do not recommend deleting significant faults to hide serious mechanical failures, as the long-term effects can be detrimental. For example, if you decide to delete a fault from a defective lambda sensor, the problem will still be present, and a richness issue can lead to rapid deterioration of the internals.