Your vehicle's onboard diagnostic system can generate numerous diagnostic trouble codes (DTCs) to identify repair issues that require attention. While the specific codes may vary depending on the make, model, and year of the vehicle, there are some common DTCs that tend to occur across different vehicles. ALLDATAdiy makes it easy to interpret DTCs and determine your best course of action, based on the latest manufacturer information.

Here are 10 examples of the most common diagnostic trouble codes:

1) P0300 - Random/Multiple Cylinder Misfire: Indicates that the engine is misfiring in multiple cylinders or the misfire is occurring randomly.

2) P0171 - System Too Lean: This code tells you that the engine is running too lean (not enough fuel) in bank 1. It could be caused by various issues such as a vacuum leak, faulty oxygen sensor, or a problem with the fuel system.

3) P0420 - Catalyst System Efficiency Below Threshold: Suggests that the catalytic converter is not operating at the expected efficiency level, which could be due to a failing catalytic converter, oxygen sensor, or other related components.

4) P0442 - Evaporative Emission Control System Leak Detected (Small Leak): Indicates that there is a small leak in the evaporative emission control system, possibly due to a loose or faulty gas cap, a damaged vapor hose, or a malfunctioning purge valve.

5) P0500 - Vehicle Speed Sensor Malfunction: Points to a problem with the vehicle speed sensor, which is responsible for providing speed information to various systems such as the speedometer, ABS, and transmission control module.

6) P0172 - System Too Rich: Shows that the engine is running too rich (too much fuel) in bank 1. Similar to P0171, this code can be triggered by issues such as a faulty oxygen sensor, fuel pressure regulator, or a problem with the fuel injectors.

7) P0301, P0302, P0303, etc. - Cylinder Misfire (specific cylinder): These codes reveal a misfire in a specific cylinder. The number after "P030" represents the specific cylinder (e.g., P0301 refers to a cylinder 1 misfire).

8) P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature): This is a flag that the engine coolant temperature is below the expected range, often due to a faulty thermostat.

9) P0401 - Exhaust Gas Recirculation (EGR) Flow Insufficient: Indicates that the EGR system is not flowing enough exhaust gas into the intake manifold, potentially caused by a clogged EGR valve or a malfunctioning EGR solenoid.

10) P0440 - Evaporative Emission Control System Malfunction: This code signals a general malfunction in the evaporative emission control system, which could be caused by a faulty purge valve, canister vent valve, or other related components.

It's worth noting that these codes provide a starting point for diagnosis, but they don't necessarily pinpoint the exact cause of the problem. Professional diagnostic equipment and expertise may be required to accurately diagnose and repair the underlying issues. ALLDATAdiy helps steer you in the right direction with factory-direct information, whether you plan to tackle the repair yourself or seek out professional assistance for more complicated problems.