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I'm getting code P0030 found out it's the heated fault of o2…

Chris , I'm getting code...
Chris , I'm getting code P0030 found out it's the heated fault of o2 sensors. I ohmed both o2 sensors pins 3&4 and they are closed loop. So i believe they are good.
Then I checked connectors pins 3&4 going to ECM with key on i was only reading about 2.56 volts on downstream and 3 something on upstream.Shouldn't the heated circuit read 12 volts on both? And if so what will be the next task to check to trace down the problem?I've already checked all grounds, battery is new fully charged, car runs but has rough startup and idles rough when cold then smooths out when warmed up.Thanks
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Answered in 1 hour by:
3/11/2018
rpmdiag
rpmdiag, Tech and Instructor
Category: Nissan
Satisfied Customers: 8,988
Experience: Since 1975
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Hello, my name is ***** ***** to Just Answer! I will be assisting you with your questions today. Give me one moment while I review this.

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The only way to accurately test the O2 sensor is with a lab scope. You confirmed that the wiring is good, but that doesn't confirm the switch activity. See attachment.

Please understand that I don't know your skill level or tools
you have to assist us. Also understand that I can't see, smell,
hear, or touch the vehicle either, so your patience is
appreciated. JA is a great Q/A site, but it does not replace a
repair shop. So please don’t shoot the messenger if I have to
deliver bad news:)
pops up. I don’t get credit for helping you until
you rate me

Thanks, Ron

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Did you have any more questions for me at this time?

Thanks again, Ron

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Customer reply replied 4 months ago
Hello Ron, I’m pretty auto savvy but not a full time mechanic just on my cars.I don’t have a lab scope but I did buy and install a new downstream O2 sensor with no luck. But I believe I’m getting low voltage from Wire harness connector pins 3 & 4. They read around 3 volts not 12.

They will read from .1 to 1.0 volts at any given time. You can have a computer problem too, but I sure wouldn't replace it yet, not know for sure what the O2 is really doing. The only proper test is with a scope, sorry you don't have one. I'd hate to see you replace a lot of good parts that would far exceed what this test would cost.

Thanks again, and please remember to rate me 5 stars now for my accurate answers. Also, keep our link in case you have any more questions after my rating.

Ron

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Customer reply replied 4 months ago
Is there a separate dedicated relay for the heated part of the O2 sensor if so do you know which one and what is your thoughts on tapping into the wiring and splicing a key 12 volt into O2 wire harness to get my full 12 volts

You're going in a dangerous direction trying that, you will almost certainly fry a computer doing that. If there were other options, I would have given them to you already.

Thanks again, Ron

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Customer reply replied 4 months ago
lets Say we’re not checking O2 sensor just the connector feeding it. Shouldn’t I be reading 12 volts out of pins 3 & 4 from ecu?
Customer reply replied 4 months ago
I’m talking about the heater pins for oxygen sensor

It's a 5 volt sensor getting it's voltage signal from the computer. The computer gets the battery voltage signals, then applies the correct voltages to the other sensors. I'm aware what you are asking.

Thanks again, and please remember to rate me and keep our link.

Ron

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Customer reply replied 4 months ago
are you saying that it may be normal that the heater circuit is only getting 3 volts with key on?

See attachment I sent you.

Thanks again, Ron

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Customer reply replied 4 months ago
Thanks a lot for diagram! Now I have learn how to decifer it.My cars code is p0030 and refers to fault in heated part of O2 or bad ECM. I believe the heater part is not working cause car has rough start and runs rough till is warmed up
Customer reply replied 4 months ago
But I think what you are saying is that if the O2 sensor is bad it want send signal to ECM to activate the heater?

I get all that you're saying, but I have never fixed an issue like this with a volt meter. Try this then, most parts stores loan/rent out tools, so see if you can get a hold of one so we can at least test the heater circuits.

Thanks again, and I'm ready to be rated now.

Ron

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Customer reply replied 4 months ago
Ok, I'll see. Tomorrow i have to leave on work trip and want be back till next Tuesday.Thanks for your help

You're welcome,please don't forget to rate me 5 stars now and keep our link. I don't get credit for helping you unless you rate me.

Thanks again, Ron

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Customer reply replied 4 months ago
After I give you a five star rating will i still be able to tell you the results of the scope next week?

Yes, I've been saying that all along, to keep our link. I will be here for any followup questions.

thanks, Ron

rpmdiag
rpmdiag, Tech and Instructor
Category: Nissan
Satisfied Customers: 8,988
Experience: Since 1975
Verified
rpmdiag and 87 other Nissan Specialists are ready to help you
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Customer reply replied 4 months ago
I found a brand new Bosch upstream o2 sensor on eBay for 36 dollars. So I will have two brand new o2 sensors installed. I will be putting them in next week.

Sorry for the delay. Okay, let me know what happens.

Thanks again, Ron

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