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Depending on the problem, it may send both codes if the issue is causing a lean condition on both engine banks. When your powertrain/engine control module receives a reading that indicates there’s too much oxygen and the ratio is incorrect, it sends an error code P0171 or P0174. A continual low voltage reading indicates a lean fuel mixture, too much oxygen. A continual high voltage reading indicates a rich fuel mixture, not enough oxygen. This is done by a continual but changing voltage signal to the computer.
![2003 mazda 6 p0171 p0174 2003 mazda 6 p0171 p0174](https://www.obd-codes.com/images/p0174.png)
These upstream sensors verify the correct air/fuel ratio is entering the engine cylinders by measuring the oxygen levels in the exhaust gases leaving the cylinders. Sensor 2 is “downstream” or after the converter. Sensor 1 refers to “upstream” sensors, or the ones near the engine and before the catalytic converter. Your bank 1 or bank 2 sensors will be referred to as “sensor 1” or “sensor 2”.
#2003 MAZDA 6 P0171 P0174 HOW TO#
The symptoms and causes will help you determine the exact issue and how to fix it. The oxygen sensor alerts your system when the condition is too lean meaning there’s too much oxygen in the exhaust. P0171 is triggered by the engine bank 1 “upstream” oxygen sensor and P0174 is triggered by the engine bank 2 “upstream” oxygen sensor. A firing order and cylinder location diagram may be needed to see which side of the engine is Bank 1 or Bank 2. Engine Bank 2 is the opposite side of the engine. Engine Bank 1 is the same side of the engine as Engine Cylinder 1. P0174 indicates Bank 2 of the engine has a lean fuel mixture. Code P0171 indicates Bank 1 of the engine has a lean fuel mixture.