The BMW Diagnostic Trouble Code (DTC) P0171 corresponds to a "System Too Lean (Bank 1)" condition. Here's what it typically means:
**P0171 - System Too Lean (Bank 1)**
This DTC indicates that the engine control module (ECM) has detected a lean air/fuel mixture on Bank 1 of the engine. In a typical inline-four-cylinder engine, Bank 1 refers to the side of the engine where cylinder 1 is located.
Common causes of a lean condition leading to P0171 include:
1. **Vacuum leaks:** A vacuum leak in the intake system, such as a cracked hose or gasket, can allow unmetered air to enter the engine, causing it to run lean.
2. **Faulty Mass Airflow Sensor (MAF):** The MAF sensor measures the amount of air entering the engine and sends this data to the ECM. If it's faulty, it can misread the airflow, leading to a lean condition.
3. **Fuel delivery issues:** Problems with the fuel pump, fuel injectors, or fuel pressure regulator can result in insufficient fuel reaching the cylinders, causing a lean condition.
4. **Faulty oxygen (O2) sensor:** A malfunctioning O2 sensor can provide incorrect data to the ECM, leading to incorrect fuel mixture adjustments.
5. **Exhaust leaks:** Leaks in the exhaust system before the O2 sensor can result in false readings and a lean condition.
6. **Dirty or clogged air filter:** A dirty air filter can restrict airflow, leading to a lean condition.
7. **Evaporative emissions system issues:** Problems with the evaporative emissions system, such as a faulty purge valve, can cause a lean condition.
