“B” codes signal body issues, such as problems with climate control, lighting, or airbags. In most cases, you will see a “P” that indicates a powertain issue, which includes a vehicle’s engine, emission, and transmission systems. The first letter (either P, B, C, or U), informs the reader of the system being affected by the problem. How to Tell What’s Wrong Using ECU Fault CodesĮCU fault codes include a letter followed by four numbers. These codes provide information on which systems are malfunctioning, where the problem is located, and the exact issue that is causing your check engine light to remain illuminated. If your check engine light comes on, the ECU fault code can tell you exactly what problem your vehicle is experiencing.ĮCU fault codes, also known as diagnostic trouble codes (DTC) are part of the on-board diagnostic (OBD II) system in your car.
When a car’s Engine Control Unit (ECU) senses a problem or malfunctioning within the vehicle, it triggers an ECU fault code that will turn on the check engine light.
