Techstream EGR Valve Blockage Data

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by jas8908, May 3, 2019.

  1. Emmanuel Isaac

    Emmanuel Isaac Junior Member

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    Posting before and after values. Cleaned at 51,500 miles. There was quite a bit of carbon but it wasn't too bad and I was able to get almost everything out with 2 cans of Brakleen and some degreaser.

    Before:
    egr before.JPG

    After:
    egr after.JPG
     
  2. ChapmanF

    ChapmanF Senior Member

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    Thanks for that! Was this also your photo (from this post) of the cooler before cleaning?

    [​IMG]

    51,000 miles seems earlier than most people do this. It appears that the cooler had some carbon 'coating' but was still flowing decently; the two cans of Brakleen improved the test value from about 19 times the minimum before cleaning, to about 22 times the minimum after.

    The reported test values can also vary a surprising amount just between tests even if you haven't changed anything. I had a reading down to 10.41 back in December when I posted that photo, but I've since had to clear codes a couple times because of other experiments, and when the EGR monitor value has completed again it has been around 16 or 17 the last couple times. It may have something to do with the kind of driving you're doing while the monitor re-runs.

    So it might be a good practice to get both the before and the after value by doing a code clear and then driving a sort of repeatable course each time until the new value is shown. These recent times I've been going out on the road, whereas in December it really wasn't being driven much.

    With the possible variation between tests being so large, the difference between the before and after numbers here seems not very big, but perhaps that's what would be expected at only 51,000 miles.
     
  3. Emmanuel Isaac

    Emmanuel Isaac Junior Member

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    Yes that is the picture taken at 51k miles from my other post. I know it is pretty premature at this mileage but I wanted to preemptively perform this maintenance as I've heard that head gasket failure is common in these engines especially in the early generations with the old intake manifold. Once I found quite a bit of oil in the intake manifold along with the misfire code, I decided to go ahead and clean out the EGR components as well for good measure.

    I believe my driving before and after cleaning should be fairly similar as I have not done much driving other than going to work and back a couple of days a week.
     
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  4. AW82

    AW82 Member

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    I did intake manifold and EGR pipe this weekend but am saving EGR valve and cooler for next weekend. I don't have tech stream but do have scan gauge 2 and a Bluetooth OBD reader.

    Is there any test I can do before/after that would be useful information here?
     
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  5. ChapmanF

    ChapmanF Senior Member

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    Some other scan tools, not just Techstream, can retrieve monitor test values. Somebody recently posted a pic of their scan tool showing the EGR flow data, only theirs displayed the pressure in psi rather than kPa. Just depends on whether the one you're using can do that.
     
  6. AW82

    AW82 Member

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    Right, but I don't think either of these devices can command EGR position like tech stream can.
     
  7. ChapmanF

    ChapmanF Senior Member

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    That was my first idea in this thread, before I discovered the monitor test retrieval, which is easier.
     
  8. AW82

    AW82 Member

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    Oh, gotcha. So that's a PID that is stored in the ECU (or wherever) and I just need to see if my OBD tool and app can retrieve the existing value before cleaning the EGR cooler and then do the same afterward, right?
     
  9. ChapmanF

    ChapmanF Senior Member

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    There was a time when I was trying to contribute to the PID reverse-engineering efforts and I boned up on all of the protocol details, but that was years ago now and most of it is not at my fingertips now. There are PIDs, but there are also different 'modes', and the monitor results retrieval might be one of those. The information is all out there, though some of it may be paywalled (SAE standards documents, for example), or on paper in your friendly library, which may have COVID restrictions.
     
  10. ozmatt

    ozmatt Active Member

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    Just wanted to post my test report

    I won't confuse this thread with unrelated nonsense but basically my car has a problem (after cleaning) I have a separate thread about it.

    I can take mine to about step 25 before any noticeable difference is detected! Screenshot_20210329-131052.jpeg

    Posted via the PriusChat mobile app.
     
  11. privilege

    privilege Active Member

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    woooo that's nice!

    I'm quoting and bookmarking this, thank you !
     
  12. AW82

    AW82 Member

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  13. ChapmanF

    ChapmanF Senior Member

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    There are some other very recent threads (don't have links handy ATM) including screenshots of the same results on a non-Techstream scanner. Monitor results are a generic category for scanners to be able to retrieve.

    The only difference seen in the screenshot of the non-Techstream display was that it was displaying the pressure in psi rather than kPa, but that's just an easy conversion.

    The repair manual also includes a section on how to interpret the results if you retrieve them on a completely generic scanner that only shows them as hex codes and doesn't even know what measurement unit to display (or so this post reports).
     
  14. AW82

    AW82 Member

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    I'll have to keep looking, then. I've searched around quite a bit and am not seeing anywhere where someone has been able to plug in and see the last EGR monitor test's "test value". A few hints that people plugged in a gauge and drove in such a way to trigger an EGR test and watched the live MAP and EGR step or commanded % gauge. Maybe that's what you're referring to?
     
  15. wheezyglider

    wheezyglider Active Member

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    Oh you can trust ChapmanF to be more precise than that at all times :). He laid that post on me, and it indeed appears that one particular scantool with "mode 6" capability has a Prius-aware interpretation of the EGR flow monitor output. From the photo I suspect that it's maybe a Nexpeak NX501?
     
  16. AW82

    AW82 Member

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    Thanks for the link. That thread did not come up in any of my searches.

    I was mostly going to do this for a data point before I clean my EGR cooler anyway, so I don't really want to buy new tools. I was hoping to find a way to do it with my ScanGaugeII or with an Android app and existing OBD Bluetooth dongle.

    Edit: Ah...I think I found it but the terminology is different. The Torque app can run a diagnostic report $06 which will show the following:
    MID:$31 TID:$bd
    - EGR Monitor Bank 1
    Max: 655.34998kPa Min: 0.99kPa
    Test result value: XX.XXkPa
    PASS/FAIL
     
    #56 AW82, Apr 7, 2021
    Last edited: Apr 7, 2021
  17. Mendel Leisk

    Mendel Leisk Sand Pounder

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    The EGR flow sensor is at the valve is determined by the MAP sensor, at the bottom of the intake manifold. Downstream, the small diameter outlets in the intake manifold, at each engine intake port, are clogging unevenly. Cylinder number one (at passenger end) typically clogs first. But the computers keep saying everything’s fine.
     
    #57 Mendel Leisk, Apr 7, 2021
    Last edited: Apr 7, 2021
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  18. wheezyglider

    wheezyglider Active Member

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    Interesting. First I've seen someone get at this using Torque.

    edit to add:
    Using my cheapo ELM327 OBD2 w/ Torque

    From the 2012:
    Screenshot_20210407-113923.png

    From the 2010 (cleaned 25K-ish miles ago): Screenshot_20210407-114143.png

    How long was that test sitting there? :oops: I can't believe I once hooked up a logic analyzer to the CAN bus trying to find this. (It was like showering in the Matrix without tools to winnow the output.)
     
    #58 wheezyglider, Apr 7, 2021
    Last edited: Apr 7, 2021
  19. ChapmanF

    ChapmanF Senior Member

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    Yeah, you can pretty much see that Mode 6 is a standard kind of query, and even generic tools now understand that that this particular MID / TID refers to an EGR test and has units of pressure. The extra section in the manual was to tell you how to munge the numbers if you were using such an old generic tool that it only dumped hex values at you.

    There isn't any flow sensor at the valve. There is an intake manifold absolute pressure sensor, which is mounted down low on the manifold, next to where the throttle body bolts on. That absolute pressure reading is what is used to prove flow.

    Because the pressure in the manifold is below atmospheric when the engine is running, that absolute pressure reading will be below 14.7 psi (and as low as 4 psi typically, at idle). When the EGR valve is opened, and gas is flowing in from another source, that reduces the vacuum (i.e., the absolute pressure reading goes up). The amount it goes up is the test value reported by the monitor.

    The effect on the manifold pressure is of course the combined effect of the EGR flow out of all four of those ports. It is a point well taken that if those four ports are differently occluded, individual cylinders can be getting too little or too much EGR while the overall test result is ok.

    On the other hand, it is only in the manifold itself that the one EGR flow path splits into four. The test value is still useful for proving the flow of gas through every component upstream of that (the cooler, the valve, the piping). That's still pretty useful, given that those upstream components are much more labor-intensive to inspect and/or clean, while removing just the intake manifold to eyeball and poke something through its four passages is a walk in the park by comparison.

    This test was definitely effective in revealing the problem ozmatt was having with the EGR valve; take a look at that test value in #50 compared to any of the more normal values seen in other posts here.
     
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  20. AW82

    AW82 Member

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