High Fuel Consumption ..The Exhaust (2)

The oxygen sensor's voltage signal is monitored by the on-board engine management computer to regulate the fuel mixture. When the computer sees a rich signal (high voltage) from the oxygen sensor, it commands the fuel mixture to go lean. When it receives a lean signal (low voltage) from the oxygen sensor, it commands the fuel mixture to go rich. Cycling back and forth from rich to lean averages out the overall air/fuel mixture to minimize emissions and to help the catalytic converter operate at peak efficiency, which is necessary to reduce hydrocarbon (HC), carbon monoxide (CO) and oxides of nitrogen (NO_X) levels even further.

The performance of the Oxygen sensor tends to diminish with age as contaminants accumulate on the sensor tip and gradually reduce its ability to produce voltage.  The sensor may also fail prematurely if it becomes contaminated with lead from leaded gasoline, phosphorus from excessive oil consumption or silicone from internal coolant leaks or using silicone sprays or gasket sealers on the engine, sulfur, oil ash and even some fuel additives.. Environmental factors such as road splash, salt, oil and dirt can also cause a sensor to fail, as can mechanical stress or mishandling


As the sensor ages and becomes sluggish, it may not allow the computer to flip-flop the fuel mixture fast enough to keep emissions within acceptable limits. If the sensor dies altogether, it will cause the feedback control system to go back into open loop with a fixed, rich fuel mixture. Fuel consumption and emissions go up, and the converter may suffer damage if it overheats. The problem may not be noticed right away because the change in performance occurs gradually. But, over time, the situation will get worse, ultimately requiring the sensor to be replaced to restore peak engine performance.

Clear signs of Oxygen Sensor failure

There are some clear signs that your oxygen sensor is no longer functioning. They can include:
1) Check engine light on
2) A rotten egg odour emitting from the exhaust.

3) A reduction in fuel economy.
4) Your catalytic converter fails unexpectedly.
5) Exhaust emissions reach undesirable levels.
6) Your engine surges, hesitates, skips etc

Keeping the oxygen sensor fresh and in good operating condition will improve fuel economy, minimize exhaust emissions, reduce air pollution, reduce the risk of costly damage to the catalytic converter and ensure peak engine performance (no surging or hesitating).

For these reasons, It is recommended to change the Oxygen sensors in newer cars (from 1996) every 100,000 miles/Km especially in Tokunbo cars or if it fails. The oxygen sensor should be considered a "tune-up" replacement item just like spark plugs

.