Downstream O2 Sensor out of bounds | Ford Explorer - Ford Ranger Forums - Serious Explorations

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Downstream O2 Sensor out of bounds

goalkeeper21986

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Explorer Sport '99
Using an OBDII scanner I noticed that my Bank 2 Sensor 2 O2 sensor was holding a constant 1.2V while Bank 1 held constant .6V. I think they are supposed to only go up to .9 V.

I've got lean code for both banks (P0171 P0174) and also P1151. I've got rough idle and total lack of power which is why I checked in the first place.

Upstream O2 sensors seemed to behave normally (less than a year old), switching between high and low. I'll try to get some freeze frame data once I learn the software better.

Since the downstream sensor doesn't feed back for fuel, is it worth replacing as a fix for my rough idle? Any thoughts?
 



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budwich

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You already answered your own question... it has no direct impact on engine operation..
 






FIND

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Just put in a MIL eliminator as long as everything else is functioning properly. All the downstream sensors do is monitor catalyst efficiency.

Unless they check emissions in your state and do visual inspections... in that case, you would want to replace it.

Your rough idle is probably a different problem, but sometimes a downstream sensor will cause it, as the computer will try and change the fuel mixture and timing to adjust the emissions. Still, probably not your problem. Check for exhaust leaks and check your plugs and wires.
 






goalkeeper21986

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I guess the question is does it REALLY only measure catalyst efficiency?

Also, since 1.25V is the max value that the computer will send, I wonder if it indicates a short in the O2 sensor circuit.
 






jimandnena

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I guess the question is does it REALLY only measure catalyst efficiency?

Also, since 1.25V is the max value that the computer will send, I wonder if it indicates a short in the O2 sensor circuit.

From the symptoms, I would start looking for an intake manifold leak or a leaking vacuum line.
 






budwich

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you can answer that question again... pull the plug on it and see what happens... monitor your data with your logger... bets are nothing will change.
 






goalkeeper21986

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Haha, thanks budwich, should have thought of that myself.
 






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