Oxygen Sensor-I don't have a location of the Bank 2 sensor, so you'll have to guess on it by determining how many sensors you have by inspecting the exhaust system from the exhaust manifold down to the catalytic converter and past the catalytic converter which is downstream. Anything before the catalytic converter is upstream.
Do you have a code that describes which O2 sensor is not responding correctly?
Test/Replace
- The sensor is threaded into the exhaust manifold.
- It can be difficult to remove unless a special anti-seize compound is coated onto its threads.
- Torque the sensor to 30 foot-pounds using a special socket.
- A sensor that is too loose or a cracked exhaust manifold can result in a lean signal to the computer.
- Check the vents in the thimble of a replacement O2 sensor.
- There should be the same number of holes and they should face clockwise or counterclockwise like the ones on the original sensor.
- Installing the wrong sensor can result in slower cross counts.
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Operation
Although the oxygen sensor is termed a sensor, in actuality it is a galvanic battery. The oxygen sensor compares the potential difference between the ambient oxygen content around the exhaust and the oxygen content present in the exhaust stream. When the exhaust sample is lean, there is more oxygen in the exhaust as compared to the atmosphere. When the exhaust sample is rich, there is less oxygen content in the exhaust as compared to the atmosphere. The greater the difference between ambient oxygen and exhaust oxygen content, the greater the voltage produced.
For the oxygen sensor(s) to operate properly, it has to reach an operating temperature of approximately 600°F before a consistent voltage potential can be generated.
The Engine Management System (EMS) determines the state of readiness of the oxygen sensors by supplying a bias voltage of approximately 400 - 500mVDC to the oxygen sensor. As the sensor begins to warm up, the voltage produced increases due to rich exhaust mixtures commanded by the EMS. When the EMS senses a return voltage greater than the bias voltage, the computer will command the fuel mixture lean. When the output voltage from the sensor drops below bias voltage levels, the computer will command a rich mixture again. When the EMS determines that the O2 sensor has responded properly and within a predetermined amount of time, it will begin using the sensor as an input to adjust fuel trim.
Many Oxygen sensors used in OBD 2 engine management systems incorporate heaters. These heaters raise the sensors up to operating temperature quickly. The sooner the oxygen sensor gets to operating temperature, the sooner the EMS can maintain closer control over emissions, economy and performance. The oxygen sensor provides the computer with necessary information to maintain favorable operating conditions for the catalytic converter. The role of the catalytic converter is to store oxygen for the reduction of HC, CO and NOx emissions. The oxygen sensor input is used by the EMS to protect the catalytic converter by cycling the air/fuel mixture rich and lean. This provides adequate oxygen for storage while maintaining cool enough operating temperatures to prevent catalyst damage.
In addition to controlling the converters operating conditions for emissions control, the computer uses the oxygen sensors to tailor fuel trim providing a balance between fuel economy and performance.
Abnormal sensor activity has a profound effect on pulse-width and fuel trim strategies. Sensor values that indicate lean conditions will cause the computer to command changes in short term fuel strategies. Conditions such as secondary misfires create excessive HC levels. This also produces high oxygen levels in the exhaust. The oxygen sensor will sense only the increased oxygen content and input to the computer will be below bias voltage levels. The computer will respond by commanding additional fuel.
OBD 2 vehicles use oxygen sensors downstream of the converter(s) to monitor the efficiency of the catalyst. When the catalyst performs properly, available oxygen is used resulting in low levels oxygen in the exhaust sample. While downstream oxygen sensors are constructed the same as upstream oxygen sensors, the values that they generate are different. With relatively richer mixtures present around the downstream oxygen sensor, voltage inputs to the computer will be above the 450mV bias voltage. If the catalyst is operating effectively, the downstream oxygen sensor will cycle when the catalyst is flooded with oxygen. Typical values from the downstream oxygen sensor(s) are between 550- 900mV at idle.
While the downstream oxygen sensor is used to monitor catalyst efficiency, the upstream sensor has a pronounced effect on performance. Lean oxygen sensor values will result in an increase in pulse-width, excessive emissions, surging, hesitation, and potentially catalyst damage. Additional fuel can cause the catalyst temperatures to rise due to an afterburner effect in the converter. The oxygen sensor is the only post combustion input to the EMS. Other malfunctioning systems affect its operation.
Improper rich indications will cause lean operating conditions that may result in loss of power, hesitation, surging, poor idle quality and possibly converter damage. Sensors that do not switch properly, or are lazy do not provide accurate information to allow the computer to properly maintain the air/fuel mixture. Faulty heaters do not allow the sensors to reach operating temperature fast enough and the vehicle may remain in open loop for longer periods of time. Malfunctioning heaters also allow the sensors to cool down during periods of extended idle.
A faulty oxygen sensor due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit can cause the following symptoms.
Related Symptoms
- Surging at idle
- Unstable idle
- Running rough off idle
- Hesitation
- Stumble
- Chuggle
- Poor fuel economy
- Spark knock
- Stalling on acceleration
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