Signs of a Bad Oxygen Sensor

Oxygen sensors, also referred to as O2 sensors, are small devices, installed in all cars and many other automobiles. Though, this device is responsible for monitoring the fuel mixture in a vehicle, many motorists are not aware of its presence in the vehicle. They notice when their vehicle runs on a low mileage, consumes too much fuel and/or when the mechanic suggests for replacing the oxygen sensor.

Role of the Oxygen Sensor in Vehicles

The oxygen sensor and the engine computer play a major role in maintaining the lowest air and fuel mixture, which in turn, lowers the fuel consumption. In this process, the oxygen sensor reacts with the unburned oxygen and generates a low-voltage signal (usually 0-1.1 volts) that determines the level of fuel content in the exhaust. When the air and fuel mixture is rich (too much fuel), the oxygen sensor signal increases and vice versa.

As per the oxygen sensor reading, the engine computer acts opposite and regulates the on-time of each injector, so as to control the fuel amount squirted in the engine. For example, if the oxygen reading is high (rich), the engine computer reduces the on-time, resulting in lowering of fuel being ejected to the engine. In contrast to this, if the reading is low (lean), the computer increases the ejector on-time and adds more fuel to the engine. This way, the oxygen sensor and the engine computer maintains the air and fuel mixture balance.

Signs of a Bad Oxygen Sensor

In case of problems with oxygen sensor, there will be no proper signal for the air and fuel mixture and the outcome is irregular emission of fuels. There are certain signs of a bad oxygen sensor, which are discussed as follows:

Poor Gas Mileage: The most common sign of a bad oxygen sensor is sudden decrease in the engine mileage. In simpler terms, the vehicle consumes more fuel than usual. In addition, the air/fuel mixture of the vehicle becomes irregular, resulting in poor fuel economy.

Engine Missing: Engine missing is usually caused when a bad oxygen sensor affects the air/fuel mixture and engine combustion. It is more evident when the automobile is idle and/or running at a very low speed.

Engine Pinging: Engine pinging is another common sign of a bad oxygen sensor, which is due to ignition of combustion gases at wrong times. A bad oxygen sensor either retards or advances the engine ignition timing, thus causes engine pinging.

Rough Idle: As oxygen sensor plays a significant role in regulating the air/fuel mixture, engine timing and intervals between engine combustion, there is no doubt that a vehicle with a bad oxygen sensor will run roughly and/or irregularly. Rough engine idle is mostly caused in vehicles that are installed with a defective oxygen sensor.

Increased Fuel Emissions: As already discussed, the oxygen sensor helps in determining the air/fuel mixture. In a vehicle with a bad oxygen sensor, the ratio is not measured accurately, which often results in an increased fuel emission.

For diagnosis of a bad oxygen sensor, sophisticated equipments such as a scan tool, digital oscilloscope or voltmeter are required. Other diagnostic methods of a bad oxygen sensor include smog test failures and OBDII code checker. The only option for troubleshooting a bad oxygen sensor is to replace it with a new one. While replacing, make sure that the oxygen sensor is appropriate to your vehicle, otherwise a wrong oxygen sensor may cause damage to the engine computer and affect the engine operation and performance.