o2 sensor

The oxygen sensor or o2 sensor measures the oxygen content in the exhaust. The more fuel placed into the combustion chamber (rich condition) the more oxygen that will be used in the combustion process. When the oxygen content in the exhaust is low, there is a chemical reaction in the sensor. This produces a higher voltage up to 1 volt. Lower voltage is for more oxygen content and can go down to .2 volts. The oxygen sensor will not work when it’s cooler than 600 degrees F. At less than this temp it displays .45 volts same being if there is a problem with the sensor. The computer will show an error (engine light)if at this value longer than what it should take to normally warm up. The o2 sensor continually shifts above and below .45 volts. If you believe the o2 sensor is bad you can test it. First run the car for 5 minutes. Disconnect only the wire running to the oxygen sensor. Then connect a ohm/volt meter with black to ground and red to the o2 wire. Set the volts to MV (millivolt) setting, the o2 should fluctuate between 100 and 1000 mv. If it dosen’t, it is not good.

 

Because of EPA regulations wanting no emissions even at startup on new cars, something had to change. A normal o2 takes awhile to heat up. An o2 sensor called a 4 wire o2 was then made. This sensor is supplied with 12 volts and heats up to aid the sensor in start up until the exhaust gets hot. Some systems now use pre catalytic converters to aid in cleaning up the exhaust at start up. Catalytic converters have the same start up problem. Without proper amount of heat it can’t operate correctly. The pre cat heats up much quicker. An o2 sensor is placed before the pre cat and after the pre cat in order to know that the pre cat is working. It will know this because there will be a significant drop in hydrocarbons (unburnt gas) at the second o2 sensor, assuming the pre cat is working. The engine goes into a “open loop” mode when the oxygen sensor is no longer working properly. This will waste gas and will not run correctly. The normal mode is a “closed loop” when the o2 works properly. Being able to check the exhaust allows the computer to know if it’s giving correct amounts of fuel to the engine as it’s running. The ecu can learn to adjust itself if an incorrect situation is known to be happening. This way the engine essentially checks itself. The fuel can very precisely be monitored and adjusted. Regular antiseize, something used on high temp threads, should not be used along with certain silicon sealers. They will damage the oxygen sensor, as a special type of o2 safe anti seize is needed.