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BMW Fault Code P0171/P0174 – Engine Running Lean
This fault code has 31 BMW specific codes asscoiated with it:
Summary, causes, symptoms and repair steps:
What does BMW fault code P0171/P0174 mean?
A BMW fault code P0171 or P0174 means that your engine is getting more air than fuel, also known as running "lean". Your BMW engine is equipped with oxygen sensors - small probes that extend into the exhaust system (usually near the catalytic converter) that measure the amount of oxygen left after combustion. If the oxygen sensors detect a higher level of oxygen in the exhaust than normal, they send a signal to your BMW's engine control module (or DME) which triggers either a fault code P0171 or P0174. Which code you get varies among different engines. Your oxygen sensors are a very important part of your BMW's emissions system, and either of these fault codes should be fixed immediately.
What causes a BMW fault code P0171/P0174 ?
The most common cause of fault codes P0171 and P0174 is a vacuum leak somewhere within your BMW's engine that is allowing excess air to enter into the cylinders. These vacuum leaks are usually around the intake manifold gaskets, the throttle body seal, or any of the many vacuum lines that service the engine. Other common causes of a lean-running BMW engine are a faulty mass air sensor, malfunctioning oxygen sensors, or air leaks in any of the intake piping.
What are the symptoms of BMW fault code P0171/P0174 ?
Common symptoms for BMW fault codes P0171 and P0174 are a rough running or surging engine, an engine that can't hold idle, engine stalls out, and a lack of power. In extreme cases, the engine may not even run.
How do I diagnose the cause of BMW fault code P0171/P0174 and fix it?
Due to the complexity of diagnosing fault codes P0171 and P0174, it is strongly recommended that the vehicle be taken to a BMW certified mechanic for diagnosis.
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