Oxygen Sensor Facts

Q. What does an oxygen sensor do?

A. The oxygen sensor sends a signal to the engine computer based on the amount of oxygen in the exhaust gas. This signal is used by the engine ECU to fine-tune the mixture to the optimum level for maximum catalyst efficiency and longevity. A worn-out oxygen sensor can cause excessive gasoline consumption, elevated exhaust emissions, accelerated catalytic converter damage failures and cause engine performance problems such as surging and hesitating.

Q. How do I know if my oxygen sensor may be damaged?

A. Unfortunately, the symptoms of a slow or even a dead sensor are not always obvious to the vehicle owner unless the vehicle fails an emissions test, a decline in fuel economy is noticed, or if driveability problems occur. Over time, exhaust contaminants accumulate on the sensing element reducing the sensor's ability to respond quickly to changes in air/fuel mixture and slowly the sensor becomes inoperable. Some symptoms of failed oxygen sensors are:

• Failed emissions test (high CO and/or HC typically)
• Damaged catalytic converter (caused by an over rich fuel mixture)
• Poor fuel mileage (caused by an over rich fuel mixture)
• Engine runs rough
• Sluggish performance

If the “check engine” light comes on while driving, check your oxygen sensor, and if necessary replace it with a new premium Bosch Oxygen Sensor.

Q. What will damage my oxygen sensor?

A. An oxygen sensor can fail prematurely if it becomes contaminated with phosphorus from excessive oil consumption, silicone from internal coolant leaks, using silicone sealant in the engine, and some over-the-counter fuel additives. Even a small amount of poorly refined gasoline can kill an oxygen sensor. Environmental factors such as road splash, salt, oil, and dirt can also cause a sensor to fail, as can thermal shock, mechanical stress, or mishandling. However as required by vehicle manufacturers, Bosch sensors are designed and tested with these extremes in mind.

Q. How can I test my oxygen sensor?

A. Unfortunately, the symptoms of a slow or even a dead sensor are not always obvious unless the vehicle fails an emissions test, a decline in fuel economy is noticed, or if driveability problems occur. Furthermore, while a dead sensor can be detected with a relatively inexpensive digital volt-ohmmeter, a slow sensor can only be diagnosed by a more expensive oscilloscope or scope meter. It is best to go to a qualified auto repair facility to have your vehicle's emission system diagnosed.