Alternate EGR tests ( P0401 )

Discussion in '80-Series Tech' started by RavenTai, Sep 22, 2006.

  1. RavenTai

    RavenTai

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    Last edited: Oct 3, 2008
  2. Claude S

    Claude S

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    Location:
    Blainville, Canada
    RavenTai, thank you fro your input, i have that same P0401 issue on my truck and did all steps per FSM and found nothing wrong (I have access to the Toyota scan tool), i checked the EGR temp with scan tool during a road test and it was fine. Now the P0401 appeared again and it is intermittent. I think i also have an intermittent vacuum modulator.

    I agree with you that Toyota make something complicated where it could have been simple and less confusing for the vacuum port on the intake manifold to the EGR.
  3. My P0401 was intermittent for ~1yr, then it came on one day and wouldn't go off. Reset, 2-trips, then MIL=P0401. Every single time. Replaced the VSV for EGR about ~4 years ago and no problems since (knock on wood)

    Great work Raven! It's OK with us if you forget about getting a real job and just continue your unshaven, unwashed, heathenistic days of posting great information here in the 80 section. :D

    -B-
  4. RavenTai

    RavenTai

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    Location:
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    LOL done, I gave up on on getting a good Job here I am moving instead, also gave up on shaving, its getting chilly here and a nice warm beard sounds good for the winter, unwashed? I cant quite handle that.

    I never got arround to testing the voltage at the VSV valve to make sure it was getting the signals it should, mainly because it is a pain to get to, based on the VSV valves track recod I decieded to just replace it, got one on the way from Dan. I already replaced the modulator and my EGR valve is good,
  5. Rookie2

    Rookie2

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    2,895
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    RT,

    What kind of vacuum guage setup have you got? Can you home-brew something together pretty easily, or did you buy the whole setup?

    BTW, I too found the VSV hard to test and was sure it was failing intermittently. Replaced it and a couple years later still CEL free, but a definitive test would be very good.

    Thanks,
    Rookie2
  6. RavenTai

    RavenTai

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    6,085
    Location:
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    I have a MityVac gauge, scroll down and look for "05511 Vacuum/Pressure Gauge" http://www.mityvac.com/pages/products_ede.asp , I think I got it at Pep boys for something like 25$

    It comes with the "T" all one would need to add is a length of vacuum line to do the driving tests. I set the gauge on the dash leaning on the windshield where I could watch it wile driving. I plugged in to different spots under the hood to watch it wile driving.

    I also borrowed a small hand operated vacuum pump from a friend to do all the static tests of the parts and checking that all the lines were clear.
  7. RavenTai

    RavenTai

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    oh also have a vacuum cap kit that has several of each size in an organizer for a few bucks, handy for vacuum system work like this
  8. Claude S

    Claude S

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    20
    Location:
    Blainville, Canada
    I replaced the modulator and haven't had the code again.
  9. How long?

    -B-
  10. RavenTai

    RavenTai

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    6,085
    Location:
    Dixie co. Florida
    Re-wite + pics

    I recently got the dreaded P0401, I started with all the tests found in two different areas of the FSM and found no solid culprit. Those tests are not good at catching intermittent problems. Maybe if I had access to the Toyota/Lexus hand held tester FSM tests would have been more fruitful. But those hand held testers are outrageously expensive and out of my reach. The FSM tests were still important though as they were the basis of later tests that I came up with.


    Some other things to try if the FSM tests do not get you there.

    Tooling

    Hand vacuum pump, a friend of mine had one of these that I borrowed, it is just a simple hand operated pump with a vacuum gauge on top.

    Vacuum gauge, I have a MityVac gauge, scroll down and look for "05511 Vacuum/Pressure Gauge" http://www.mityvac.com/pages/products_ede.asp , I think I got it at Pep boys for something like 25$ It comes with the "T"

    6’ or more of vacuum line, the hard lines on the 80 are .155” OD, 3/16 (.189”) vacuum line seals but does not hold on very tight works OK for temporary testing, if you could find some 5/32 vacuum line (.159” IIRC) it should work better.

    Female vacuum caps, 5/32 would best.


    Modulator

    The Vacuum modulator is the brains of the EGR system, it has two vacuum inputs from the throttle body to watch throttle plate position and one pressure input from the exhaust to watch engine load, and from these three inputs it outputs a vacuum signal to the EGR valve.

    This vacuum signal is nil at idle and provides more vacuum as the throttle plate opens more, at about mid way it reaches maximum vacuum, as the throttle is opened further past aprox mid point the vacuum sharply decreases and is again nil when the throttle is wide open.

    Alternate tests for the Modulator,
    If you blow into the port on the bottom (exhaust pressure port) and air comes out of any of the other ports then the diaphragm is bad, if you can see any carbon in the system then the diaphragm is bad. With the cap and filter off the modulator and the engine running I could feel exhaust pulses coming out of the breather hole in the top of the modulator, later on I cut my old modulator open and found the pin hole leak in the diaphragm,

    I replaced my green top modulator with the new blue top, even though it was “bad” and needed to be replaced it was not the source of my P0401. It still passed all the FSM tests and provided the proper vacuum signal to the EGR valve.

    The leaking exhaust gasses would have eventually fouled the whole system with carbon witch would have added other problems on top of the existing problems making troubleshooting even more difficult, but I caught it early enough where the fouling was limited to just the modulator and its filter.


    EGR Valve

    The EGR valve is pretty simple, it has a diaphragm and a spring fighting each other, as the vacuum sent to it increases the diaphragm moves the valve towards open, as the vacuum decreases the spring pushes the valve towards closed. The amount of EGR flow is therefore proportionate to vacuum applied.


    Alternate EGR valve tests,
    plug one of the two ports with a vacuum cap and apply vacuum to the other with a hand pump, it should hold that vacuum without leaking down, this tests the diaphragm for leaks, if you do this with the engine running it will also stall the engine testing that the valve actually opens and that exhaust gasses do flow. this is an alternate version of the FSM test. If the valve opens and closes and the diaphragm does not leak the valve is good.

    Line System

    I also checked to make sure all of the vacuum lines were clear including the hidden path from the VSV to the throttle body under the intake by drawing vacuum through them with a hand vacuum pump, They were all wide open. Many have found these plugged with carbon, I also plugged and applied vacuum to different sections to make sure there were no vacuum leaks.

    EGR temp sensor

    This is the ECU’s only eyes into EGR operation, when EGR flows it gets hot, early FZJ80’s did not have one unless they came from California. If the temp sensor does not get hot when it is suppose to it will throw a P0401, If the temp sensor is hot when the EGR is not suppose to be running (during the early stages of warm up) then it throws a P0402.

    I did not bother pulling and cleaning my temp sensor when I was chasing my P0401, the factory seal looked too good to mess up, I did check its resistance per the FSM wile in place and it was in spec, no need to disturb that seal when it is very unlikely to solve the problem. YMMV

    VSV valve

    The VSV valve's only task is to veto EGR operation, as far as I can tell it only does this during the early stages of warm up. it is a simple electric open/close solenoid controlled by the ECU, when it is closed the EGR system is armed and is controlled by the modulator, when it is open the VSV allows atmospheric pressure from the throttle body to flow into the EGR valve defeating the vacuum signal from the modulator.


    The VSV is expensive over a weeks worth of groceries, I had no problem replacing it IF it was the culprit but I wanted to be certain before I laid down the $ for a new one, I needed a way to watch the EGR system in action all together wile driving, that is where the FSM calls for the hand held tester, Since I knew that my EGR valve worked and did not leak if I watched the amount of vacuum it was being fed to it I could tell what it was doing and why the ECU was unhappy.

    Driving Test

    I removed the clutch master plug in the firewall and ran a vacuum line from the engine bay into the cab and hooked it to the vacuum gauge.

    Use it one of two ways,

    One way to hook it up reads the pressure to the EGR valve with everything intact.

    Make a 5” or so vacuum line with a ‘T’ in the middle one end goes on the EGR valve, the other on the nipple on the intake manifold and T in the sense line to the cab, (see pic 1)


    When you first start up cold the VSV is open so you will see no vacuum, shortly after the vacuum should start to follow throttle plate position

    Idle, no vacuum,
    Cruise, lowest pressure, on a slight downhill as low as 12 or 13 inches of mercury on steep down hills the pressure would increase, and uphill it would also increase
    Regular acceleration ~5 inches of mercury
    Moderate throttle to WOT, no vacuum

    If you are not getting any vacuum the Modulator is either not providing any or more likely the VSV is open defeating what is being provided.

    To test with is witch the other way is to watch just the modulator alone: remove the short line that runs from the nipple on the intake manifold and goes to the EGR valve, plug the intake nipple and hook the sense line from the cab to the EGR valve, (see pic 2)

    Now you can drive around and see the signal that the modulator is sending to the EGR valve without interference from the VSV,

    If it works as it is suppose to this way but did not before then most likely your VSV is bad, if you still have no vacuum the modulator is bad or there is a plugged line or a vacuum leak somewhere.

    Be aware that because the VSV is out of the picture and unable to kill the EGR during warm up that it will throw a P0402.
    EGR1.jpg EGR2.jpg EGR3.jpg
  11. Chris Wilcox

    Chris Wilcox

    Messages:
    307
    Location:
    NB, Canada
    Would someone with a working EGR system have data or be willing to test the vacuum to egr diaphram during driving conditions. I'd like to get confirmation that you also observe the behaviour that Raven did.
    That being:
    " Idle, no vacuum,
    Cruise, lowest pressure, on a slight downhill as low as 12 or 13 inches of mercury on steep down hills the pressure would increase, and uphill it would also increase
    Regular acceleration ~5 inches of mercury
    Moderate throttle to WOT, no vacuum"
    Please also list if you are using green or blue modulator.

    You would need to hook your system up like the 2nd picture above.

    I am getting 4-5" max during cruise and regular accelaration and can't figure out why.
    Thanks,
    Chris

  12. Chris Wilcox

    Chris Wilcox

    Messages:
    307
    Location:
    NB, Canada
    OK, Pretty sure I've determined the cause of my P0401. Intermittent VSV for EGR valve. This seems to be a possible failure mode from other posts, of which I've read most of on this code. If you perform the shop tests and everything checks out perfect, you have cleaned all the lines etc etc and you can not figure out what is going on, it may be reasonable to suspect a vsv that quits working once underhood temperatures cause it to heat up.

    After many hours of testing and thought, I finally bit the bullet and wired up the car to test this thing.
    I had laptop with obdII software to monitor codes, monitors and engine parameters.
    Vacuum gauge tee'd into the line from EGR to manifold (VSV), as per Raven above.
    Breadboard with two led's. These were wired directly from the exposed VSV connector, by the manifold, and indicated if I had 12VDC power to the VSV at all times and the other indicated if the ECU was grounding the ground side of the VSV, ie calling for it to block flow.

    This setup allows me to monitor VSV operation (if EGR is getting vacuum or not) and monitor if I have a wire short and if ECU is functioning properly.

    Initially everything worked perfect but after 10 minutes of driving the lights kept working but the vacuum gauge stopped moving. If I idled down a long hill (currently cool here ~10degC) the VSV would start working again. Drive some more and it quits. All the while the ecu was properly demanding VSV functions.

    I'm going to change it and probably at the same time see if I can determine why it might quit when hot and mount the new one in an easier location.

    I hope this helps someone else in their endless quest to fix the P0401.
    Chris Wilcox
    Last edited: Sep 20, 2008
  13. Chris,
    You certainly are tenacious and I can appreciate that.
    -B-
  14. Chris Wilcox

    Chris Wilcox

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    307
    Location:
    NB, Canada
    Got my new VSV from cruiserdan (thanks) and have this P0401 thing figured out.
    This time, to be sure I was replacing the correct part, I moved the old VSV inside the cab along with OBDII laptop, multimeter indicating demands of ECU and a vacuum gauge. Turns out you don't really need the vacuum gauge as you can hear the clicking of the VSV when it is sitting right beside you on the center console!
    After some time driving around I was doubting my earlier analysis, however then I turned the heat on full, to simulate engine environment, and held the VSV in front of the vent. It wasn't long before it quit working once I added a bit of heat. I checked the multimeter and it was asking for the VSV to work but it wasn't responding. Swapped in the new one and all was well again.
    I can't say why they quit with age/temperature but they seem to and it is repeatable. Very hard to diagnose as well using FSM instructions. Also plays tricks on you driving around. If you do short in town trips the code will disappear because the thing doesn't get warm enough to quit. Then you go for a long drive and the light pops on. I've been dealing with this type of thing for months.
    Now I am not sure if I should relocate this VSV to an easier to access location, that is also cooler, or just put it back where it was and deal with an eventual failure.
    VSV removal was from below and through the "hole" once the brace was removed. Somewhat difficult but much less daunting than intake removal.
    Chris
  15. RavenTai

    RavenTai

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    Location:
    Dixie co. Florida
    Same exact problem as mine, VSV that fails when heated and the FSM tests cannot find it. you certainly went further to prove it, nice work.

    my FJ-62 has the VSV's mounted on the fender away from the heat, only problem is it makes for a much messier engine, less room to work and generally untidy looking with vacuum lines piled on like a plate of spaghetti.
  16. beno

    beno 33030-60450 Moderator Supporting Vendor

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    Nice RT....as always done with the expertise of an aircraft mechanic!

    ;)

    By the way, what the heck was that Tajik Air bird doing over at the south end of TechOps this past week....MRO or are we takin' her?

    ;)

    -o-
  17. RavenTai

    RavenTai

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    Are you here in ATL or were you just passing through?

    MRO, just the paint job, our paint crew is temporarily shutdown at least for our own, something about the budget and the quarter, contract work on the other hand kept running as that is money in not just out,

    Last I saw it, (Monday night/Tuesday morning maybe?) it was sitting in bay 11 just about done, they were trying to figure out the placards, they got a complete set of them but they are in Russian and nobody could figure out where they go. does pack of weird a's and backwards 3's say "danger powered inlet" or "emergency open" they were looking for a translator.

    It is owned by International Lease Finance, I hear they own about a thousand aircraft, we are trying to get all of their work, good customer so far, they want it fixed and fixed right and they pay, so far I think it is working they keep sending more work.

    did you see the contract DC-10 in bay 8? that's where I work (only 2 weeks left)
    Last edited: Oct 3, 2008
  18. Chris Wilcox

    Chris Wilcox

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    307
    Location:
    NB, Canada
    P0401 has been fixed for almost a month now since the VSV swap. I also mounted it on the fender which should keep it cool and easy to change or troubleshoot if need be.
    Chris
    IMG_4205.jpg IMG_4206.jpg
  19. Good move Chris. :D

    I wish Toyota put that VSV there in the first place.

    -B-
  20. scoop

    scoop SILVER Star

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    149
    Location:
    Atlanta
    RavinTai I just saw your post and see that you work in the same area. I work in Toc 3 Bay 11. You can leave yet this 401 code is getting the best of me and I have to pass emissions test in a month.

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