Checking VSV for EGR easy way P0401

Discussion in '80-Series Tech' started by Alex Kogan, Mar 19, 2008.

  1. Alex Kogan

    Alex Kogan

    Messages:
    41
    Location:
    Portland, OR
    Well I got bit with that bug too. Sorry if I missed something, although most common culprit has been long identified - VSV, most of ways to check its operation are rather tedious. Here is my easy way.
    Disconnect VSV connector from main engine harness. Check for continuity between two terminals with yellow wires on opposite side. You must have something like 30-35 oms. No continuity = bad VSV.
    [​IMG]
    Otherwise rig up something to connect those terminals to battery.
    [​IMG]
    Then disconnect a vac hose from EGR valve. If you can blow air through or suck it out of it when terminals are connected to battery = bad VSV. (when disconnected - air should be able to flow).
    [​IMG]
    Ones VSV is removed you might want to double check findings but I really fail to see why Toyota in shop manual recommends to remove intake plenum to just check VSV.
    If all checks out, look elsewhere.
    On the side note. I've seen a advice to clean passage through intake manifold. Well, clogged up passage could only conceivably cause code P0402 not P0401 since it would induce too much vacuum above membrane of EGR valve thus opening it too much. Role of VSV is to prevent vacuum built up unless ECU decides that now is a good time to close it.
    Just my $0.02
    Last edited: Mar 19, 2008
  2. bpenn1980

    bpenn1980

    Messages:
    907
    Location:
    Los Angeles
    Awesome, this saves me a big pain in the arse. Like you said, the only testing methods I've read mean pretty much removing the VSV. If I'm going to be doing that I might as well get the starter rebuilt, PHH knocked off and replace the fuel filter :D

    I like your way and will be employing it on my rig this weekend. Gracias
  3. MoJ

    MoJ Moderator

    Messages:
    3,254
    nice write-up
  4. superhawk

    superhawk

    Messages:
    22
    Location:
    Milwaukee, WI
    quick question

    Man this was helpful. After I threw a code 71 (1994) I was frightened to see how many things could be wrong with the EGR system. I just did this test and registered about 29.7 ohms, so I am guessing that is close enough to the range. Anyway, my question is this: Is there anything of mechanical nature that could go wrong with the VSV, or is it safe to assume that along as there is enough continuity the VSV is OK.
  5. Bluetribal

    Bluetribal SILVER Star

    Messages:
    4,402
    Location:
    Sandy Eggo
    I just threw this code last Friday before heading to Baja, truck did great in Baja for the weekend but now it's time to make that engine light stop looking at me. Thanks for this and hopefully I can test it out this weekend.
  6. Ted44

    Ted44

    Messages:
    202
    Location:
    Charlottesville, VA, USA
    With one caveat.

    Some here, me included, have experienced a VSV for EGR that is intermittent in its function. Of course, this means it is bad in my book, but it may not always show up as bad when testing it.

    FWIW
  7. Imagery

    Imagery

    Messages:
    337
    Location:
    Beaumont, Texas
    All I can say is Good Luck. I've been looking at my CEL, PO401 for a couple years now and I have tried to track it down myself with the mothods outlined in the FSM with no success. I have had two shops attempt to find and correct it, the first one replaced the EGR valve itself and the last one, just a couple weeks ago, replaced the VSV for $150 and neither one worked. The light stayed off each time they cleared it and came back on after metting the criteria of running at 52 mph for however long, three times and then it comes back on. I am not going to pay anyone else to try to find it so the next thing I plan on doing is removing the intake manifold and cleaning out all passages ect, then see if that works. I surely don't want to pay someone to do that because if it doesn't work, i'll have to keep bringing it back until they finally give up. It's kind of frustrating to not be able to resolve the issue but I don't feel like it is causing any problems to the engine performance and fuel mileage.
  8. bpenn1980

    bpenn1980

    Messages:
    907
    Location:
    Los Angeles
    I'm Code 71 free! I found the plug (looks different on a '94) and went to pull it. Wouldnt you know it, the damn thing wasnt fully pushed on! I pulled it, blew it out and plugged it back in. 363 miles free of that damn CEL, and I averaged 16.6 mpg for over 200 miles!

    :beer:
  9. landtank

    landtank SILVER Star

    Messages:
    17,230
    Location:
    Groveland MA
    I posted a while back about those two wires, however they are only reliable if the resistance is within spec. If the resistance is out of spec you still need to pull the VSV as there is another connector between those test points you show and the VSV itself.
  10. Alex Kogan

    Alex Kogan

    Messages:
    41
    Location:
    Portland, OR
    Yes (second part of the post), you need to hook up those wires to battery and make sure that you can't blow air through VSV via hose connecting it to EGR valve. Having resistance means that coil in VSV is not shorted but it may still not be able to close internal valve preventing vacuum build up in EGR valve.
  11. MLX450

    MLX450

    Messages:
    586
    Location:
    Silverdale, WA

    Did you replace the modulator?

  12. Alex Kogan

    Alex Kogan

    Messages:
    41
    Location:
    Portland, OR
    Just an update.
    Kudos to CDan the parts man. New VSV is in, MIL is off, EGR emission readiness monitor passed.
  13. teeth geek

    teeth geek

    Messages:
    4
    Great Info on this thread

    Newbie here. Signed up to say thanks for the test information. I tested mine and got infinite resistance so off with the VSV using info from IH8MUD. After replacing the VSV, :steer:I drove it and scanned the OBD II and have only one readiness code left so I'm off to the biannual Smog Check tomorrow. Thanks again.
  14. johnnyllama

    johnnyllama

    Messages:
    117
    Location:
    Winter Park FL
    Thanks!
  15. S.CarolinaFZJ80

    S.CarolinaFZJ80

    Messages:
    2,207
    Location:
    Charlotte
    Thanks. I will try this test as I constantly get the 0401 code, even after the PO replaced VSV, EGR & modulator 13,000 miles ago. I even removed the upper intake plenum, cleaned/reamed all holes/ports and replaced the tubing a few months ago and to no avail.
  16. powderpig

    powderpig SILVER Star

    Messages:
    1,006
    Location:
    Boulder Foothills, CO
    If everything also check out, check the temp sensor. I have replace two of these in the last year. Everything check out, had me stumped for a little bit. Then remember the computer only know the gas is flowing or not if the temp sensor is working.
  17. Flank

    Flank TLCA Independent Rep - Central and Mountain States

    Messages:
    1,726
    Location:
    Flower Mound, TX
    Have you pulled your throttle body to see if the port from the EGR to TB is clogged? Mine was pretty bad.
  18. Round rock cruiser

    Round rock cruiser

    Messages:
    3
    P0402 code ewww

    Hey guys I've been reading your thread about this code, here may be a silly question does it narrow it down any if I'm getting terrible gas mileage as to egr, vsv, etc. ?
    Any help very much appreciated.
    I have a 97 landcruiser
  19. Flank

    Flank TLCA Independent Rep - Central and Mountain States

    Messages:
    1,726
    Location:
    Flower Mound, TX
    Not really. The EGR system is an emissions control system. That being said, some of us have realized better performance after servicing the EGR, mainly do to the fact we've also cleaned out our intake plenum, throttle body and changed out vacuum tubes. Many people actually just disable the EGR (illegal in most areas) and don't see any change in either mileage or performance.
  20. Pin_Head

    Pin_Head

    Messages:
    11,819
    Location:
    OC, CA
    For that code, the first thing you would want to do is make sure the EGR valve is not stuck open. Check for a rough or low idle and see if the idle improves when you whack the valve with the handle of a screw driver. If not, then check the valve for function by pulling a vacuum on the EGR valve actuator. It should stall or idle rough with vacuum applied and idle smoothly when you release the vacuum

Share This Page