How to Resolve BMW 120408 Fault Code?
2 Answers
BMW 120408 indicates an oxygen sensor malfunction. Use a diagnostic tool to measure the voltage. If the voltage remains static between 0.4-0.5V, it confirms sensor failure requiring immediate replacement. Detailed explanation follows: 1. Function: The oxygen sensor serves as a critical component in electronic fuel injection systems, playing a vital role in maintaining proper engine operation and effective emission control. When the oxygen sensor or its wiring fails, it not only causes excessive emissions but also deteriorates engine performance, potentially leading to symptoms like stalling at idle, irregular engine operation, and power loss. 2. Location: Typically there are two oxygen sensors: the front sensor (pre-catalytic converter) positioned at the exhaust manifold, and the rear sensor (post-catalytic converter) located behind the three-way catalytic converter. The front sensor regulates air-fuel mixture ratio while the rear monitors the catalytic converter's operational status.
When I see the BMW 120408 fault code, it reminds me of my own car experience. This is usually an issue with the engine management system, such as a problem with the air-fuel ratio adjustment. Common causes include a dirty oxygen sensor or a faulty mass air flow sensor. First, I would use a diagnostic scanner to read the specific error message. After confirming, I would check for vacuum leaks in the engine bay and try cleaning the mass air flow sensor. If the light still comes on, the sensor itself might be faulty and need replacement. Don't ignore these issues, as they can lead to increased fuel consumption and affect driving performance. When working on it yourself, remember the safety steps: turn off the engine and disconnect the battery's negative terminal. It's advisable to buy a basic tool kit—cheap and convenient. However, if you can't fix it, it's better to visit a repair shop promptly to avoid worsening the problem.
