There are several factors that can affect the normal functioning of the oxygen sensor. It is important to isolate if it is the oxygen sensor itself or some other factor causing the oxygen sensor to behave abnormally. See Course 874 Technician Reference book for more information.
A contaminated oxygen sensor, will not produce the proper voltages and will not switch properly. The sensor can be contaminated from engine coolant, excessive oil consumption, additives used in sealants, and the wrong additives in gasoline. When lightly contaminated, the sensor is said to be "lazy," because of the longer time it takes to switch from rich to lean and/or vice versa. This will adversely affect emissions and can produce driveability problems.
Many factors can affect the operation of the oxygen sensor, such as a vacuum leak, an EGR leak, excessive fuel pressure, etc.
It is also very important that the oxygen sensor and heater electrical circuits be in excellent condition. Excessive resistance, opens, and shorts to ground will produce false voltage signals.
In many cases, DTCs or basic checks will help locate the problem.
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