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P1800....o2 sensor harness disconnected

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Old 02-29-2016, 01:18 PM
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P1800....o2 sensor harness disconnected

Hi everyone I purchased a 2003 manual maxima which I didnt see had some harnesses disconnected while I was inspecting it. The car is showing p1800 on my scanner, which I knew before purchasing. As well as alternator and battery light are on. So.....before throwing parts at it ie VIAS selenoid(p1800), new battery alternator, battery,etc. I want to know where these two disconnected harnesses go. One(white headed connector, six prong) is connected to the downstream(?) o2 sensor in the pictures below. The other(blue headed connector, four prong) looks like it comes off the main wiring harness above the valve cover. I'd like to know where they are connected before fixing the alternator, vias selenoid, etc. The car starts and drives though if that matters. Thank you guys.












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Old 02-29-2016, 02:46 PM
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Dumb dumb tried installing a wideband sensor. Blue connector is for the O2.

It was throwing the code for bad cat and they must've thought a sensor off a newer VQ/QR would work.
Trash the cats immediately.

Last edited by Child_uv_KoRn; 02-29-2016 at 02:51 PM.
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Old 02-29-2016, 03:13 PM
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Strangely the car doesn't throw a check engine for the o2 sensors,cat, etc., the only code is p1800(VIAS Selenoid). What would be your advice on returning back to factory, this is my first nissan just learning about the vq35's. So basically I should take out the white headed o2 sensor/harness and install one for this year and it should clip onto the blue one? Could there be any major damage done by the previous owners running the car with o2 sensors un-clipped? Thanks.
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Old 02-29-2016, 04:58 PM
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Originally Posted by sick-speed
Strangely the car doesn't throw a check engine for the o2 sensors,cat, etc., the only code is p1800(VIAS Selenoid). What would be your advice on returning back to factory, this is my first nissan just learning about the vq35's. So basically I should take out the white headed o2 sensor/harness and install one for this year and it should clip onto the blue one? Could there be any major damage done by the previous owners running the car with o2 sensors un-clipped? Thanks.
It takes a while for those codes to pop up. They probably reset the ECU before you came. The secondaries are not needed. They're only for emissions.

You need to read through a lot of the threads. Precats have to go before they blow the motor.
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Old 02-29-2016, 08:58 PM
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Depending on the mileage of the motor the damage is more than likely already done. BUT you can stop it from doing any more. Either gut the cats or buy headers.
Get into the habit of checking your oil every second day for at least a month. if your not noticing that its burning any then check it once a week AT LEAST.
I've replaced mine and it doesn't burn a drop but still checked it every week when she was up and running.
Get a new OEM secondary sensor from rock auto or the dealer if you like blowing money inappropriately. Make sure its for the right location as well.
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Old 03-01-2016, 05:34 PM
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Thanks for the help guys, looks like ill be replacing the o2 sensor and ill go from there.
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Old 07-15-2016, 03:42 PM
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Does the P1800 error also cause a P0420 error ?
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