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Closed Fuel Loop. Rear o2 sensor no voltage. po422 main catalyst.

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1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
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1997 - 2000 V70, V70 AWD
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nico416
Posts: 31
Joined: Thu Dec 08, 2016 7:39 am
Year and Model: 98 s70
Location: Toronto

Closed Fuel Loop. Rear o2 sensor no voltage. po422 main catalyst.

Post by nico416 »

So Ive fixed quite abit of things on this beast to get it pretty well in order, But the main concern is still chasing the lambda light.. po422

-Manifold leak was detected and repaired with new flex pipe. Original accordion design was leaking and apparently even the 98/99 late redesigns used the newer flex pipe design even fcp i see the new flex pipe design..

-Brand new o2 sensor installed in rear. there was some work done to rethread it to fit properly there aswell.*

-Brand new j hose, evap hose, Fuel filter & fuel cap.

-New plugs. Original wires and probably cap too though. I have some 2011 bougiecords/cap/rotor on my 850 wagon, but for 100$ maybe buy a new set of these if it is something that could cause me po422.

Notes:
I have a hard time figureing out this o2 sensor voltage and really have a feeling its the issue here, so my story is i got a brand new o2 sensor 2 months ago, installed it, and i had all those leaks for manifold ect. But I had noticed the entire time im getting no voltage to the rear sensor, when i ask the people at bosch they claim they have never had a new defective o2 sensor and they are telling me to check the power delivery to it, how would i go about that so i can rule it out?

There is currently no used sensors around for me to play with otherwise i would buy the o2 wrench and just play with it myself with a used working one from my wagon even to prove that its the sensor.

Main things im seeing here through my obd2 and scanmaster software is this Closed Fuel Loop in the fuel system, And I notice no Rear o2 sensor voltage absolutely 0v which to me is strange, It does give me a po422 for main catalyst efficicency and people use that to just say oh your cats bad. pointing me in the direction of a cheap small cat that i really dont want to trust. I know for fact lots of people use these cars on original cats and havent had to swap them and i guess im just assuming so id like to know for sure, But if im getting no voltage from the rear sensor at all, is it really a bad cat because it seems that data not going to the comp could tell it bad catalyst efficiency, i see the front sensor go pretty crazy trying to give voltage. ?

I could take a drive with anumber of grapphs on that scanmaster software if that would help. just tell me what fields to bring up.

I dont smell any weird cat smells and i have a hard time thinking its the cat, the 97 850 with 572000km has the original cat, and o2 sensor voltage, its has a Cel for the manifold leak and honestly should of just repaired that one instead of chase this rabbit hole to hell of an s70..

Both a 98 t5 and a 97 850 with a CEL light for seperate issues both show me rear o2 voltage of about 0.4 volts so im really troubled.

I bought the Bosch plug from FCP.

This car is a '98 non turbo s70.
97 850 GLT platinum edition 225km - RIP Headon accident
97 850 wagon non turbo SE 570km - RIP. No ac, still runs, but started using as a Parts car
98 S70 non turbo SE 237km - Daily Driver Runs nice, but po422 nightmare.
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abscate
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Re: Closed Fuel Loop. Rear o2 sensor no voltage. po422 main catalyst.

Post by abscate »

Main things im seeing here through my obd2 and scanmaster software is this Closed Fuel Loop in the fuel system, And I notice no Rear o2 sensor voltage absolutely 0v which to me is strange, It does give me a po422 for main catalyst efficicency and people use that to just say oh your cats bad.
Cripes. The cat efficiency is measured by the rear O2 sensor, so once you get that straight I bet that code goes away.

Find the wiring diagram off the webs, look for 12 VDC on the rear O2 sensor plug for the heater. If you used a universal O2 sensor or you had to make wiring mods to get it installed, you probably need another one - the right one.
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Herb Goltz
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Re: Closed Fuel Loop. Rear o2 sensor no voltage. po422 main catalyst.

Post by Herb Goltz »

I have had a new Bosch sensor that was defective on a 240 I used to own-- the heater circuit was bleeding voltage over to the sensor circuit-- I was seeing about 1.4V on the sensor output instead of the expected swing between about 0.15-0.85V. It is possible that you have a dud. Do you have 12V at the harness plug for the rear sensor heater? Check your fuses. Why was there re-threading work for the sensor-- did removing the old one gall the threads? If you actually had a dead cat but working sensors, I'd expect the waveforms of the front and rear sensors to look similar. A steady 0.4V sounds about right for a functioning front sensor and cat.
nico416
Posts: 31
Joined: Thu Dec 08, 2016 7:39 am
Year and Model: 98 s70
Location: Toronto

Re: Closed Fuel Loop. Rear o2 sensor no voltage. po422 main catalyst.

Post by nico416 »

The 2nd guy i had show it, claimed he saw voltage, how come im not seeing voltage with my software. its also the 2nd guy to point to a dead cat

What graphs of data do i need to pull up the car drives fine, thats why i cant figure out the rear voltage no voltage. ill take it on a drive today and try to pull some more data and post to maybe help figure this issue out.
97 850 GLT platinum edition 225km - RIP Headon accident
97 850 wagon non turbo SE 570km - RIP. No ac, still runs, but started using as a Parts car
98 S70 non turbo SE 237km - Daily Driver Runs nice, but po422 nightmare.
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