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Rear O2 Questions V70-XC70 1998

posted by  jadnhm on  Sun Dec 19 14:53 CST 2010
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last visit: Tue May 22 18:03 CST 2012
[RELATED]

Hello Fellows.

I have been chasing a P0133 for a couple of years now and really getting frustrated.

This code maps to both Volvo codes 435 (front O2 slow to respond) and 436 (rear O2 compensation - whatever that means).

I have replaced the front O2 sensor twice with the bosch direct-fit replacement and still get the code.

I am very sure I don't have any vac leaks, though I have not smoke tested yet (been meaning to make a DIY smoke tester but haven't gotten around to it yet). I have replaced every vac and PCV line on the car recently and see no wearing/softening/etc.

I am also very sure there are no exhaust leaks, though I have not smoke tested yet (see above). I have done the 'plug the end and look for smoke' test and see no exhaust escaping.


I did the test as described by tmannian (http://www.brickboard.com/AWD/volvo/1457038/850/code_436new_o2_sensor.html) in a recent thread about a similar problem. I found the rear O2 did NOT respond as predicted by the test. It read 0.48V the entire time no matter what I did to introduce a vac leak or make the mixture rich by clamping the return fuel line. I was able to watch both sensors output in real time on my scan tool.

"Great!" I thought. I'll just replace the rear O2 and be done with this.

I today replaced the rear O2 sensor with one that bench tested fine. I am not sure what the sensor I pulled is (maybe a walker?) but the one I put in was a bosch.

I then ran the rear O2 tests again and saw the EXACT SAME THING - 0.48 through all tests.

Any ideas about what's going on? The MIL hasn't come back on yet because I haven't really taken the car anywhere (down the road to the in-laws). I suspect it will though.

Does this point to a bad CatConv? A bad FPR?

Any and all ideas are welcomed.
--
1998 V70 AWD->FWD Turbo 200k+









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    Rear O2 Questions V70-XC70 1998

    posted by  tmannian on  Sun Dec 19 16:01 CST 2010
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    last visit: Sat Sep 20 10:31 CST 2014
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    Just want to be sure, you waited until the car fully warmed up to check the voltage? When the sensor is preheating the voltage will be around .4 so if you're reading early, it might just be in preheat mode and not pay attention to what you're doing with rich/lean.
    --
    If you're not driving it "like its stolen," are you really driving?








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      Rear O2 Questions V70-XC70 1998

      posted by  tmannian on  Tue Dec 21 02:10 CST 2010
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      last visit: Sat Sep 20 10:31 CST 2014
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      Just wanted to say this is incorrect. I misread the signal specs, and the preheat value is .4V, but the data line will be ignored and given the average of the sensor (.47-.48) until it is fully warmed up.
      --
      If you're not driving it "like its stolen," are you really driving?








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      Rear O2 Questions V70-XC70 1998

      posted by  jadnhm on  Mon Dec 20 00:54 CST 2010
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      last visit: Tue May 22 18:03 CST 2012
      [RELATED]

      Thanks for the reply.

      I did wait, but I also kind of thought I would wait until I could run the tests again after a decent drive to be sure.

      I will report back then.

      Any other thoughts?
      --
      1998 V70 AWD->FWD Turbo 200k+








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        Rear O2 Questions V70-XC70 1998

        posted by  jadnhm on  Tue Dec 21 01:34 CST 2010
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        last visit: Tue May 22 18:03 CST 2012
        [RELATED]

        My wife had the car all day yesterday and I took it for an errand first thing this morning. I noticed right away the MIL was on and I had been planning to run my tests on the rear O2 again after a good warm-up drive, so when I got it home I hooked up my scanner to see what I could see.

        There were two DTCs stored:
        p0141 (EFI-522 - Rear HO2S Preheating)
        p0136 (EFI-153 - Rear HO2S signal)

        These are both new - I've never seen either one before.

        From those codes it seems likely that I may have not installed the new(er) rear O2 sensor properly. I'll pull it out again this afternoon and do a very careful reinstall.

        I ran my rear O2 tests anyway and saw only 0.48v no matter what I did - this was after a 25 minute drive....


        --
        1998 V70 AWD->FWD Turbo 200k+








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          Rear O2 Questions V70-XC70 1998

          posted by  tmannian on  Tue Dec 21 02:08 CST 2010
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          last visit: Sat Sep 20 10:31 CST 2014
          [RELATED]

          I wonder if the connections isn't quite there, and its just using its saved value (in your case .48) constantly. Throwing both codes means its a possibility.

          I don't think you could install the sensor improperly, as I thought there were two notches on one side and one on the other. They're only little notches so its possible its upside down if you had to force it in. Hopefully that's all it is, otherwise I think you might have to start checking the wires between the ECM and the O2 sensor, it would seem like something isn't getting through...

          To test the connector: Pin 1 is furthest from the U locking mechanism, and pin 4 is closest.. Test resistance between pin 4 and ground, should be about 50kOhm (ignition off, wait 5 minutes so main relay is closed.. O2 sensor disconnected). Pin 3 and ground should be 200 Ohms. Next step is verifying that the sensor works.. Start checking at the receptacle side and if you get a different number check the back end, perhaps you have a loose wire or two.
          --
          If you're not driving it "like its stolen," are you really driving?








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            Rear O2 Questions V70-XC70 1998

            posted by  jadnhm on  Tue Dec 28 01:02 CST 2010
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            last visit: Tue May 22 18:03 CST 2012
            [RELATED]

            I pulled the rear O2 I installed and found my connections were not done properly. I went out and bought a new 260W solder gun and redid everything, and put it all back together.

            I first waited for the engine to heat up and found the rear O2 sensor actually started responding!! Fluctuating with the engine and tests as it should!

            Everything has been fine since. I was doing some travelling for the holidays and put ~700 miles on the cars in the last week and no MIL and fuel mileage is better too.

            I'm really hoping this is the end of this story.

            --
            1998 V70 AWD->FWD Turbo 200k+








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              Rear O2 Questions V70-XC70 1998

              posted by  jadnhm on  Sun Jan 9 13:58 CST 2011
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              last visit: Tue May 22 18:03 CST 2012
              [RELATED]

              I have had no further problems with the MIL since this repair was completed. My gas mileage is up a bit too thankfully.

              This test procedure really helped me locate my problem in the rear O2, and I'm very glad I did both the tests and the repair.

              I'll keep everyone posted if anything else comes up to do with this problem or repair.
              --
              1998 V70 AWD->FWD Turbo 200k+







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