Troubleshooting Oxygen Sensors
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What they do
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An oxygen sensor is a device that monitors the exhaust gasses exiting a vehicle. Its job is to see if the engine is running too rich, too lean or just right. A bad air to fuel mixture can cause the engine to run badly, and affect gas mileage adversely. In some states, having an oxygen sensor that is in good operating condition is necessary for smog inspections. They have been in use since 1980 on most vehicles.
Where they are
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Locate the exhaust manifold of the vehicle, and then follow the pipe down. The oxygen sensor is between the engine and the catalytic converter. It looks similar to a sparkplug with an electrical wire coming off of it, and is threaded into the exhaust pipe.
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Inspect the wire
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An oxygen sensor will not work properly if the connection is full of grease or soot. Also, keep all the wiring attached to the oxygen sensor away from the exhaust pipe, because it can cause failure or a fire. If the wire has bare spots or looks broken, replace the sensor.
Inspect the sensor tip
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After the engine has warmed up, turn it off and unscrew the oxygen sensor from the exhaust pipe, being careful not to burn yourself in the process. Look at the tip of the oxygen sensor to make sure it isn't covered with carbon deposits or burnt badly. If these signs are not present, rethread the sensor into the exhaust pipe.
Test the electrical
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Using a digital volt meter, test the connection with the vehicle running and warm. The optimum air to fuel mixture ratio is 14.7:1, and the oxygen sensor will maintain this ratio if it is operating correctly. If the engine is running lean (more air than fuel), the meter will read between 0.1 and 0.5 volts. If the engine is running rich (more fuel than air), the meter will read between 0.6 and 0.9 volts, with the ideal reading being 0.5 volts. If the reading is erratic, it could mean that the engine has a vacuum leak, or that the oxygen sensor is going bad. Look for vacuum hoses that have come off of their ports on the engine before replacing the sensor. An average oxygen sensor will last between 30,000 to 50,000 miles before they read inaccurately under normal circumstances.
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