Photo by follettmotors_com These days, most cars have engine control systems that respond to inputs from various sensors. These systems work to adjust and regulate emissions, engine performance, and other major functions.
These sensors are required to give precise information to prevent unnecessary fuel consumption, emission failures, and driveability problems.
Oxygen sensor is one of the key sensors that gives important signal to computer system in the engine.
Oxygen sensor is usually called O2 sensor. It was first introduced in 1976 on 240 Volvo vehicle. In 1980, California issued its emission rules that required lower emissions. During this time more and more cars were equipped with O2 sensors.
And in 1996 the government issued OBD-II regulations. The auto manufacturers responded it by producing cars with multiple oxygen sensors, some had as many as four.
In order to monitor unburned oxygen as the exhaust exits the engine, an O2 sensor is attached in the exhaust manifold. This monitoring is done to adjust fuel mixture.
When the sensor senses low oxygen it means the fuel mixture burns rich, the system will respond by injecting less fuel.
When the O2 sensor signals high oxygen,it means the fuel mixture burns lean, the system will respond by injecting more fuel.
There are several other factors that may affect the fuel mixture condition (lean or rich). They are engine coolant temperature, throttle position, air flow, engine load, barometric pressure, and air temperature.
All these factors are monitored by sensors.
But the most essential information is the signals that are retrieved from O2 sensor.
So if there are problems with the oxygen sensor, this may generate significant impacts on the engine and its performance.
The process of computer system regulating fuel mixture based on inputs from oxygen sensor is called “feedback control loop”.
Photo by lumachrome This loop works as follow:
The computer system reads the signal from oxygen sensor and respond by adjusting the fuel mixture. This action will change the fuel / oxygen ratio, because the condition changes the O2 sensor reading changes. The computer system will then respond to this change. The system works on and on like this, flip flop back and forth from lean to rich.
This loop enables catalytic converter to perform at highest efficiency while maintaining the proper balance of overall fuel mixture. The whole mechanism will produce minimum emission.
Well does this system look complicated to you ? Yes It is complicated, but fear not what you need is just understand the big picture.
When a cold engine is first started, the oxygen sensor usually sends no signal,if this is the case the computer system will adjust to rich fuel mixture. The same condition also happens when the O2 sensor fails. This situation is referred to as “open loop” operation.
If the engine is unable to enter closed loop (ideal condition, flip flop from lean to rich), the engine will run in over rich condition that will waste much fuel and increase emissions.
This may happen when oxygen sensor fails to send signal once it reaches operating temperature or the O2 sensor’s signal is lost.
Another possibility is a bad coolant sensor. In order for the computer to decide whether or not to enter closed loop, it will also check the engine coolant temperature.
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