What is O2 / Oxygen Sensor, (Lambda)

Introduction to the oxygen sensors
Oxygen sensors are a product that have been around for over 20 years, but most drivers do not even know they are one or more of these devices on their vehicles - let alone what it does.
The only time that motorists are aware of the oxygen sensor is a Check Engine light when there is a code and an O2 sensor problem or their vehicle does not test, because the emission of a sluggish or dead O2 sensor. If their engine is running or is not using too much fuel, someone would tell them they might need a new O2 sensor. But in most cases they will have no idea how to diagnose or test this mysterious little device that often is blamed for all kinds of driveability and emissions ailments. That puts the sales of professional knowledge about the components.
FUNCTION
So what exactly does the O2 sensor do? It controls the mixture so the engine computer to adjust the air / fuel ratio to the lowest possible emissions and maintaining the best fuel economy. The O2 sensor does this by responding to unburned oxygen in the exhaust. The sensor generates a small voltage signal (usually less than 1 volt), which increases when the air / fuel mixture is rich, and decreases as the air / fuel mixture is lean. It behaves like a rich / lean switch the computer each time the fuel mix changes constantly signals.
The way the computer provides a balanced fuel mix is the opposite of what the O2 sensor reading. If the O2 sensor reads rich (excess fuel), the computer reduces the on-time of each injector pulse to reduce the amount of fuel injected into the engine. This makes the mixture go lean. Once the O2 sensor detects this and gives a reading lean (insufficient fuel), the computer reacts and increases the on-time of each injector pulse to add more fuel. This back-and-forth balance leads to an average mixture that is pretty close to ideal. This is the "fuel feedback loop" that the current vehicles to maintain very low emission levels, and the O2 sensor is the key sensor in the loop.
The computer uses different sensor inputs, like that of the coolant sensor, throttle position sensor, manifold absolute pressure sensor, airflow sensor, etc. to further refine the air / fuel ratio as needed to meet the changing circumstances . But the O2 sensor, the key input that determines what happens to the fuel mixture. So if the O2 sensor not reading right, it screws up everything. Usually, a bad O2 sensor reads low (lean), which causes the engine to run rich, pollute too much and use too much gas. A low reading may be caused by several things: age, pollution, and wiring connection, or a compression ignition or engine problem.
AGING O2 SENSORS
If an O2 sensor ages, it is not responding as fast as it once did. The increased delay, the sensor is slow and prevents the engine from keeping the air / fuel mixture in close balance. If the engine burns oil or coolant leak develops an internal, the sensor element which polluted the sensor to fail. Back when leaded gasoline was still available, a single tankful of leaded fuel, most O2 sensors killing a few hundred miles. That is why the government finally eliminated leaded fuel.
Because the sensor reacts to oxygen in the exhaust and no fuel, no problem with the engine that allows unburned air to the cylinders by an O2 sensor can also be tempted to read lean. A running engine spark plug or a leaky exhaust - even a leak in the exhaust manifold gasket - is enough air in the exhaust to screw up the sensor readings. It will not damage the sensor, but it will be a rich running condition that the emissions and fuel consumption hurts to create.
HOT, HOT, HOT
Something else you should know about the O2 sensors is that they are too hot (617-662 degrees F) to produce a voltage signal. It may take several minutes for the exhaust to heat the sensor, so most O2 sensors on newer cars have a built-in electric heater circuit to the sensor to obtain the temperature as quickly as possible. These are mostly three-wire and four-wire O2 sensors. The one-and two-wire O2 sensors are heated. If the heater circuit fails, it will not affect the operation of the O2 sensor once the exhaust is hot but the computer will immediately go into a closed loop, which can lead to a vehicle emissions test is not.
DIAGNOSIS AND REPLACEMENT
O2 sensors can be diagnosed in several ways, most of which require special equipment. A scan tool or code reader is required to O2 codes to withdraw from most newer vehicles, although manual flash codes "are available on older vehicles. If an O2 sensor problem is suspected, the sensor response and output voltages are monitored with a scanner, a digital voltmeter or oscilloscope. If the tests confirm the O2 sensor is dead or slow, replacement is the only option Restore. There is no way to "clean" or "rejuvenate" a bad O2 sensor.
Replacement sensors have the same basic type as the original (heated or unheated) and have similar performance characteristics and heater wattage requirements. Installing the wrong O2 sensor affect engine performance and possible damage to the heater control circuit in the engine computer. So make sure you have the O2 sensor replacement supplier offers.
Do not go by appearances alone. Some replacement O2 sensors have an OEM-type connector and cabling require no modifications to install. Others (usually the "universal type O2 sensors) require splicing the sensor wires into the original connector harness.
Replaced
To maintain peak engine performance, there is no need to wait until the sensor can not be replaced. Some experts now recommend replacing O2 sensors at specific times kilometers for preventive maintenance. The recommended interval for one or two wires unheated O2 sensors on 1976 through early 1990 applications to 30000 to 50,000 miles. Heated three-and four-wire O2 sensors on mid-1980 to mid-1990s applications can be changed every 60,000 miles. And on 1996 and newer OBD2 vehicles, the recommended replacement interval is 100,000 miles.
How much?
Four cylinder and six cylinder cylinder engines typically have only one O2 sensor in the exhaust manifold. With V6 and V8 engines, there is an O2 sensor for each cylinder bank, or a total of two (one in each exhaust manifold).
On 1996 and newer vehicles with OBD2 (On Board Diagnostics II), there is one or more additional O2 sensors after the catalyst to increase the efficiency of the converter control. If a vehicle has a dual exhaust, there will be a downstream O2 sensor on each side. So a V8 car with dual exhaust will usually have a total of four O2 sensors.