Diagnostic Test Code (DTC) P0171 is defined by SAE J2012 as "System Too Lean Bank 1".
This is what is known as a fuel trim code. Something is causing the fuel trim on bank 1 of your engine to reach a predetermined maximum set point. This can be caused by many things including vacuum leaks, malfunctioning injectors, a fauly mass airflow sensor, or even a catalytic converter that is clogged up.
If there are no fuel trim problems on the opposite bank, then there is a problem that affects only one bank. It is necessary to access the fuel trim data to correctly identify the problem. You may have fuel trim problems on the opposite bank that have not yet set a code. If the fuel trim data proves that there is no problem on the opposite bank, then this rules out several possiblities like the mass airflow sensor, as it will affect BOTH banks, not just one.
To put it simply: Proper diagnosis required.
SOURCE: 1997 buick lasabra engine code >po171
The trouble code is related to a lean engine fuel trim problem. This particular code can be caused by a vacuum leak, low fuel pressure or faulty MAF or MAP. Check for vacuum leaks first, if you cant find any broken or cracked hoses, you might want to take it to a good shop and have live data read to determine if there is a component defective.
PO171 OBD2 Code basically this means that an oxygen sensor in bank 1 has detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1. The P0171 is one of the more common trouble codes.
his code is triggered by the first downstream (front) O2 sensor. The sensor provides a reading of the air:fuel ratio leaving the engine's cylinders, and the vehicles powertrain/engine control module (PCM/ECM) uses that reading and adjusts to keep the engine running at that optimum ratio of 14.7:1. If something is not right and the PCM cannot maintain the 14.7:1 ratio, but rather there is too much air, it triggers this code.
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