EVAP & transmission problems related?

Discussion in 'General Motoring' started by cz, May 23, 2008.

  1. cz

    cz Guest

    Vehicle Specs:
    2000 Saturn SL2 with just over 14,000 miles

    Since October my 'Service Engine Soon' light has been coming on with
    some degree of frequency. My service technicians say the problem is
    in the EVAP system. Initially I was told to turn my gas cap at least
    three clicks after pumping gas. When that didn't work, the gas cap
    was replaced. When that didn't work, some temperature related element
    (a thermostat if memory serves correctly) was replaced. I think there
    was one other replacement after that. Things seemed to be going
    better (as measured by almost a month without a 'Service Engine Soon'
    light coming on) until a month and a half ago when my transmission
    (rear & 2nd gear to be specific) blew and I had to have it replaced.
    This morning the 'Service Engine Soon' light popped on and sure
    enough, the technicians are telling me that it's the EVAP system
    again. At this point they say they have run every test known and
    consulted with Saturn engineers. They ultimately replaced one of the
    two solenoids, simply because the only parts of the EVAP system that
    haven't been replaced are the solenoids, so they're hoping this fixes
    it, and if it doesn't, then they'll simply fix the other solenoid.

    Since I've never personally known someone with either EVAP problems or
    a blown transmission, and since most of the people I know are driving
    cars older than mine and those cars have had significantly less engine
    problems than mine, I can't help but wonder - is it possible that my
    transmission blew because of the mystery EVAP problem/s?
    cz, May 23, 2008
  2. cz

    Bob Shuman Guest

    In my opinion, the answer to your question is "No" ... it is not likely the
    two are related.

    Bob Shuman, May 23, 2008
  3. cz

    Oppie Guest

    My experience with a '01 lw300 having an evap code was that the vent
    solenoid was not closing properly. The valve is normally open when the
    engine is off and closes to allow the purge solenoid to clear vapors from
    the canister. I replaced the vent solenoid three times, the first two being
    at one year intervals. The last replacement has been in place for almost
    three years now.
    The Evap system test, which is preformed regularly by the onboard
    computer, closes the vent solenoid, opens the purge solenoid and monitors
    the vacuum in the tank. At some point, the purge is closed and the vacuum
    sensor monitors the pressure in the tank. Depending whether it holds at
    level, falls slowly or falls fast, it gives either a normal, slow leak or
    gross leak code respectively. My car kept throwing the gross leak code which
    was equivalent to a loose gas cap.

    Many of the codes that cause a MIL light to come on will cause the engine to
    run in open loop. This in turn messes up the finely tuned relation between
    engine management and transmission control. In short, the engine may seem to
    run fine but transmission shifts like crap.

    Hope my little dissertation was useful - Oppie
    Oppie, May 23, 2008
  4. cz

    cz Guest


    I was actually following your explanation until "This in turn messes
    up the finely tuned relation between engine management and
    transmission control." Does this mean that an 'engine running an open
    loop' could cause transmission failure?
    cz, May 27, 2008
  5. cz

    Oppie Guest

    I meant to say that there is a finely tuned relationship between an engine
    running in closed loop and the transmission/powertrain controller. When the
    engine is running in open loop, This tuning is ignored and all reverts to
    limp home mode.

    I can't speak for all systems, but when I have gotten engine codes, the
    traction control light (on the TRAC button) turns off and the transmission
    shifts very hard. I would expect that if that type of shifting should
    continue for a long enough period, it may cause a failure in the

    I had to laugh when I read your description of their troubleshooting. It
    shows a minimal understanding (if that) of the diagnostic systems. The bit I
    wrote was almost verbatim (albeit from memory) from the factory service
    manual. Any tech with access to a tech II or equivalent should be able to
    read the canister vacuum sensor value and make a reasonable determination.
    For that matter, putting a gauge on the test port can do almost the same
    thing to monitor when a evap canister test is invoked.

    Oppie, May 27, 2008
  6. cz

    -Cronus- Guest

    Transaxle people... TransAXLE...
    14k miles?
    I cant follow this post... Without providing codes a verifiable
    diagnosis for these problems would be futile. In the future write this
    stuff down and get second opinions while the issues are occurring.
    -Cronus-, May 31, 2008
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