O2 sensor loses its reading speed gradually as it ages. Due to a longer time needed for reading, the sensor becomes sluggish and the air and fuel mixture is not in a good balance.
The O2 sensor element may become contaminated whenever the engine has an internal coolant leak or it burns oil. This will cause the sensor fail to read.
When the era of leaded gasoline was available, most cars that were loaded with a single tankful of leaded fuel have their O2 sensors failed in a few hundred miles of journey.
Due to its characteristic, oxygen sensor doesn’t react on fuel but only to oxygen inside the exhaust. So if there’s any engine problem which allows unburned air to go through cylinders.
It will trigger the oxygen sensors into reading low fuel. These are 2 common problems that may cause an O2 sensor to read low fuel (lean):
Leaky exhaust valve. For example, a leak in the exhaust manifold gasket.
A Misfiring spark plug.
These problems won’t damage the sensor but your engine will waste the fuel because of oxygen sensor misreading. It will also generate unnecessary emissions and expensive fuel economy.
One important thing to notice is oxygen sensor requires hot temperatures to generate a voltage signal (617 to 662 degrees of Farenheit).
It takes a few minutes for the exhaust to heat up the sensor. In order to overcome this condition, many newer cars have built in electrical heater circuits to help the sensor reaches the required temperature rapidly.
Whenever the heater circuit fails to work as expected,it will take a longer time for the exhaust to reach the minimum temperature.
As the result, the O2 sensor will need to wait until the exhaust is hot enough before taking proper readings, thus it will delay the computer from applying balanced ratio of air/mixture.
If this happens, your car won’t be able to pass emissions test.
How to Check and Replace Oxygen Sensors
There are several ways to diagnose O2 sensors, most of them need special equipment. For newer vehicles you need a code reader or scan tool to retrieve O2 codes.
In older vehicles there are manual “flash codes” available for diagnosing.
If the codes that are read refer to O2 sensor problem, you may monitor the sensor’s voltage output and response by using a scan tool, digital oscilloscope or voltmeter.
If the tests show that oxygen sensor is sluggish or dead then you need to replace it, this is your only option. You can’t rejuvenate or “clean” a damaged oxygen sensor.
You should use a replacement sensor that has same basic type as the original one (unheated or heated).
You should also make sure that it has the same heater wattage requirements and performance characteristics.
Engine performance can be affected if you install the wrong O2 sensor. The worst case is it could possibly damage your heater control circuit in the engine computer.
So what you need to do is read carefully your O2 sensor supplier’s replacement listings and follow the requirements and specifications.
Don’t buy an O2 sensor based on its appearance alone. Several replacement oxygen sensors require have wiring connections that comply to OEM-type so you don’t need to modify them to install.
While others (Universal Type O2 Sensors) need slicing the sensor wires into the original connector harness.
Replacement Intervals
In order to keep your engine in healthy and peak condition, you should replace the O2 sensor when it reaches certain interval limit.
Experts recommend to replace unheated one or two wire oxygen sensors on 1976-1990s engines every 30,000 to 50,000 miles.
For heated three and four wire O2 sensors on mid 1980s to 1990s, they should be replaced every 60,000 miles.
For cars produced on 1996 and newer OBD2 cars, the oxygen sensors should be replaced every 100,000 miles.
V6 and V8 engines have two oxygen sensors in each exhaust manifold or one oxygen sensor for every cylinder bank
Engines with straight six cylinder and four cylinder usually have only one O2 sensor. It’s placed in the exhaust manifold.
There is one or more additional oxygen sensors are attached after the catalytic converter of 1996 cars and newer ones with OBD2 (On Board Diagnostics II) . These O2 sensors are used to monitor converter efficiency.
For cars that are equipped with dual exhausts, there is one downstream O2 sensor on every side. So, there is a total of four O2 sensors inside a car with V8 engine and dual exhausts.
Bosch 15733 Oxygen Sensor, Universal Type Fitment
Bosch 13540 Oxygen Sensor, OE Type Fitment
Bosch 15730 Oxygen Sensor, Universal Type Fitment
Nonin GO2 Achieve Fingertip Pulse Oximeter – Blue
Denso 234-9009 Oxygen Sensor (Air and Fuel Ratio Sensor)
Denso 234-9005 Oxygen Sensor (Air and Fuel Ratio Sensor)
Bosch 15727 Oxygen Sensor, Universal Type Fitment
Oxygen sensors make cheap fuel economy possible. It works by regulating and adjusting fuel / air ratio. The computer system inside the engine injects a proper amount of fuel based on the oxygen sensor readings so that it won’t waste unnecessary fuel and pollutant.
http://www.metacafe.com/watch/yt-QQ393gnvm-k/
Photo by Honda CB77 Restoration Your Honda Civic needs electrical spark generated by the spark plug wires in order to run properly. A distributor assembly is used by Civic to deliver power to the spark plugs. The plugs, they run between your engine and the distributor. If the plug wires has problem, the engine won’t be able to run. Hard starting and misfiring are common problems that are caused by poor spark-plug. Spark-plug wires should be checked and replaced if necessary every 30,000 miles. Most auto parts stores sell the replacement plug wires. 
