# resistance of oxygen sensor



## isrummell

im wondering if anybody knows what the resistance of the oxygen sonsor behind the catlytic converter is supposed to be


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## isrummell

its a 98 chevy 1500 4.3


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## octaneman

Hi isrummell

There are no resistance readings taken on a O2 sensor.
There are two types of tests you can do to an an oxygen sensor: 1) on the car , 2)off the car (bench test). The easiest method is to do it on the car but it would require the sensor to reach 600°F and a scan tool to get the accurate readings. The bench test is more of a quick test to determine if it works or not. To do the bench test you will need a propane torch and a DVOM. The main idea is to connect the red leed of the meter to the black wire of the sensor, and the black leed of the DVOM to the body of the sensor.


Turn on the meter and set it to the lowest voltage scale, light the torch and place the tip of the oxygen sensor in the flame. Since there is no oxygen, the sensor will produce .9v or 9/10th's of a volt within 1 minute. This will indicate a rich mixture because the voltage is climbing. As you pull away from the flame,the voltage must drop within 3 seconds to it's original reading ,the voltage drop indicates a lean mixture. 

If there is no reading or if the sensor voltage is not changing, then it indicates a bad or sluggish O2 sensor that needs replacing. 


Note: Some O2 sensors have a heating element with more that 1 wire connected. Always connect to the black wire on the sensor to do the bench test.


Good Luck!


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## isrummell

how would i test the one BEHIND the cat. it doesnt test rich or lean just how the cat is doing


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## octaneman

Wrong. 

The downstream O2 sensor does not say how the cat is doing, if the catalytic is blocked the O2 sensor will only register a P0420 code. The downstream sensor opperates the same way as the upstream O2 sensor. The only major difference is the downstream sensor voltage should remain at a constant .45v or higher and not changing as fast ( cross counts) as the upstream O2.


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## isrummell

hey thanks i may be able to use the info for what im doing


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