Tech: Understanding OBDII Engine Systems and Fuel Mixture Control

When the Check Engine Light comes on due to the fuel mixture related error codes P0171 and P0172, or your 3rd generation Toyota with either the 3.4L V-6 or 2.7L 4 cylinder engine is just not running like it should, the oxygen sensor and the Mass Air Flow Sensor (MAF) are common suspect items. They do work closely together in performing their function, but without additional information on exactly how they do their job, it can be confusing to determine which might be at fault. Either sensor is too expensive to do a trial and error replacement to determine which might be causing a problem. This article will examine the role these sensors play, along with the Main Engine Control Unit to maintain proper fuel/air mixture control.

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