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O2 sensor, '98 volvo S70

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O2 sensor, '98 volvo S70

Postby Baer1964 » 01 Sep 2010, 19:29

I am working on a 1998 Volvo S70 with a 2.4L nonturbo. I replaced the front oxygen sensor(customers request). The car was getting a po130 code and black smoke out the tail pipe. After replacing the front sensor and turning off the check engine light, the car ran ok. Soon afterwards engine light came back on with po131 code. This time I checked the live data and front o2 sensor was running about .310 volts and the rear sensor was reading 0 volts. I replaced the rear sensor and it is still getting 0 volts. I swapped the wires, connecting the wiring harness for the front sensor to the rear sensor, and rear harness to the front sensor. Now front sensor reads about .610 volts and the rear still reads 0 volts. This tells me both sensors are working, but the ecm is not seeing a reading on the rear harness. I unplugged the ecm and ohmed the wiring and all wires are good. I hate to just say bad ecm. Can some one advise me on a way to check this any further and why am I not getting any voltage reading on the rear O2 sensor harness.

Thanks
Rondy
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Re: O2 sensor, '98 volvo S70

Postby misha » 01 Sep 2010, 21:49

Do you still have black smoke from the exhaust after replacing sensor?

If you do,you can try with disconnecting negative battery terminal for about 15-20 min. in order to reset fuel trim.
'97 850 2.5 20v /fully equipped/ Motronic 4.4 / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic/petrol+LPG
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Re: O2 sensor, '98 volvo S70

Postby FCPGroton » 02 Sep 2010, 00:24

I think it would be best to leave the battery disconnected for about 20 minutes either way to be honest.
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Re: O2 sensor, '98 volvo S70

Postby Baer1964 » 02 Sep 2010, 12:26

Have already disconnected battery for a couple hours. Battery went dead and was replaced. Yes it does have black smoke when operating on front sensor. If you connect front harness to rear sensor the black smoke goes away.
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Re: O2 sensor, '98 volvo S70

Postby misha » 06 Sep 2010, 01:00

Baer1964 wrote:If you connect front harness to rear sensor the black smoke goes away.


Strange thing.

I guess that somebody you bought the car from messed something up with o2 connectors.Maybe he just connected front o2 sensor where the rear o2 should be by mistake.

Hmmm,is car working properly when you connect front o2 sensor to the connector of the rear one & the rear o2 sensor on front o2 connector?

If it does then leave it like that,maybe that is the proper connection....like i said before...could be that previous owner connected them wrongly.
'97 850 2.5 20v /fully equipped/ Motronic 4.4 / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic/petrol+LPG
History of Volvos in the family:
'71 144 De luxe
'73 144 De luxe
'78 244 DL
'78 244 DL
'79 244 GLE
'85 340 GLS
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Re: O2 sensor, '98 volvo S70

Postby Baer1964 » 06 Sep 2010, 21:30

I have traced the wiring out. O2 sesors were connected correctly. If yoou connect the harness for the front O2 sensor to either sensor I get a readig on the scan tool. If you connect the wiring harness for the rear O2 sensor to eitherr sensor I get a 0 volt reading. I have traced the wires to the ECM and wiring is good, no short to ground or opens. Also no short to other wiring.
The car is getting black smoke out of tail pipe when front harness connected to front sensor. When front harness is connected to rear sensor, black smoke goes away, but I am concerned about car running to lean.The only thing I can think of to repair this problem is to replace the ECM
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Re: O2 sensor, '98 volvo S70

Postby misha » 06 Sep 2010, 23:44

I usually don't recommend Volvo stealerships(dealerships),but you could visit them if you want to solve your problem.

I think they are the only one who probably can solve your problem,but that could be expensive.

Visit them and see what they have to say about it and how much the repair would cost.

It could cost you a lots of money...or it just can be very cheap repair.

Good luck!
'97 850 2.5 20v /fully equipped/ Motronic 4.4 / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic/petrol+LPG
History of Volvos in the family:
'71 144 De luxe
'73 144 De luxe
'78 244 DL
'78 244 DL
'79 244 GLE
'85 340 GLS
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Re: O2 sensor, '98 volvo S70

Postby ziggy55 » 07 Oct 2010, 20:43

Im having the exact same issue with a 1998 Volvo S70. I tried another ECU and the same issue still. Did you solve yours?
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Re: O2 sensor, '98 volvo S70

Postby t5ftw » 07 Oct 2010, 22:06

Baer1964 wrote:I am working on a 1998 Volvo S70 with a 2.4L nonturbo. I replaced the front oxygen sensor(customers request). The car was getting a po130 code and black smoke out the tail pipe. After replacing the front sensor and turning off the check engine light, the car ran ok. Soon afterwards engine light came back on with po131 code. This time I checked the live data and front o2 sensor was running about .310 volts and the rear sensor was reading 0 volts. I replaced the rear sensor and it is still getting 0 volts. I swapped the wires, connecting the wiring harness for the front sensor to the rear sensor, and rear harness to the front sensor. Now front sensor reads about .610 volts and the rear still reads 0 volts. This tells me both sensors are working, but the ecm is not seeing a reading on the rear harness. I unplugged the ecm and ohmed the wiring and all wires are good. I hate to just say bad ecm. Can some one advise me on a way to check this any further and why am I not getting any voltage reading on the rear O2 sensor harness.

Thanks
Rondy


ECU may just not report rear O2 sensor voltage when it detects a problem (e.g., front O2 sensor). So, it does not necessarily mean that rear sensor is bad. Your problem sound similar to my problem, but not identical. My guess is that you need new front sensor and adapter cables for both front and rear O2 sensors. Check my thread. I have a link to a TSB about the problem that I experienced.
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Re: O2 sensor, '98 volvo S70

Postby xtrattitude4u » 07 Oct 2010, 23:15

Ive been told by several people that the rear O2 sensor is only for monitoring that the catalytic converter is functioning properly, and doesn't affect fuel trim. The ECU may only check this sensor periodically.
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Re: O2 sensor, '98 volvo S70

Postby ziggy55 » 08 Oct 2010, 00:27

Can you please provide me the link for the TSB. This issue is driving me nuts. I have replaced both sensors and tried a another ECU, rear sensor still always reads 0V in ECU. I scanned an identical car and getting readings from the rear sensor.
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Re: O2 sensor, '98 volvo S70

Postby t5ftw » 08 Oct 2010, 00:30

xtrattitude4u wrote:Ive been told by several people that the rear O2 sensor is only for monitoring that the catalytic converter is functioning properly, and doesn't affect fuel trim. The ECU may only check this sensor periodically.


That was my belief too. However, I also heard some people saying rear O2 sensor affects fuel trim in thier Chrysler and Toyota. I don't know if this is the case with our Volvo, but I went through a problem like this. I had a front O2 sensor code constantly keeps coming back and an intermittent rear O2 sensor code. I replaced front O2 sensor twice. Didn't fix it. So, I disconnect the rear O2 sensor cable. Car ran fine. Finally, I replaced rear O2 sensor. Problem solved. I read the OPs post again. I think my problem may not exactly the same. In my case, rear O2 sensor voltage only drop to 0V after CEL comes on. Until then, it still reported some number like 0-0.5V.
Last edited by t5ftw on 08 Oct 2010, 00:56, edited 1 time in total.
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Re: O2 sensor, '98 volvo S70

Postby t5ftw » 08 Oct 2010, 00:32

ziggy55 wrote:Can you please provide me the link for the TSB. This issue is driving me nuts. I have replaced both sensors and tried a another ECU, rear sensor still always reads 0V in ECU. I scanned an identical car and getting readings from the rear sensor.


http://www.volvoforums.com/forum/showth ... ht=25-0033

The TSB is for 1999-2002 cars, but I heard earlier cars had similar issue and different kit is used
My mechanic printed out more information about the problem. I only have a hard copy. If you have access to iATN board, search for "1999 Volvo V70, Emissions/MIL" by Bruce Oct 4, 2004 and "2000 Volvo S80, MIL" by John Apr 12, 2007.
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Re: O2 sensor, '98 volvo S70

Postby chernobyl1 » 02 Apr 2011, 14:42

I actually have the exact same issue on my "98 V70 wagon. When I pull up the OBDII info from the computer it shows a normal voltage for the front oxygen sensor, but no voltage for the rear sensor. The ECM hasn't been throwing any codes related to the rear sensor, so I figured it must be standard for these cars... maybe.

On a possibly related note, I have been getting pretty crap mileage (<20 mpg mostly highway) and poor throttle response from this same wagon. I can't seem to track down any vacuum leaks, so I was wondering if I hooked up a vaccuum pump to the tree, is there a certain level of vacuum that I should be looking for?

Stocking up parts for a PCV, T-belt, and suspension job on this wagon in the next month, but I'd love it if I could track down this problem first!
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