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Old 12-11-2017, 08:01 AM
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2006 Pathfinder
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Voltage is supposed to range anywhere between 0 volts to about 1 volt on a given oxygen sensor. This shows the rich to lean cycling pattern of the sensor. The ECM compares the frequency of the cycling between the front and rear sensors on each bank, which set in front of and behind the upstream catalytic converter. An efficiently working catalytic converter will see during cruising conditions an approximate ratio of 2:1 for the number of cycles of the front sensor compared to the number of cycles of the rear sensor. If the ratio is close to 1:1, then the converter is not efficiently working at breaking down the exhaust gases and the ECM will trigger a code. Sometimes you can "fake out" the ECM by installing a spacer or "CEL eliminator" at the rear sensor, which pulls the rear sensor element partially out of the exhaust stream to give it a false reading.
In most cases when there is a P0420/P0430 code and no other codes, no exhaust leaks, no intake leaks and the engine is running normally, it is typically the catalytic converter, itself, that needs to be replaced to fix the problem. If you don't live in a state that mandates California-style emissions inspections, you can purchase an aftermarket converter which is significantly less-expensive that a genuine Nissan part ( is a good source; I've had good luck with Walker converters).
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