LHS Cooling system fans

Discussion in 'General Motoring' started by Hank NB, Nov 2, 2005.

  1. Hank NB

    Hank NB Guest

    Hiya Folks,

    Here's a puzzler for you. The culprit: 1997 LHS 3.5 Liter. When idling,
    the temperature climbs higher than normal. Checked fans and they don't
    start until higher temp reached then run until engine cools some but not to
    normal level. (They cut out early.)

    Problem comes and goes (intermittent). Checked all connections (computer to
    relays; computer to temp sensor; etc.). Replaced both high and low speed
    relays. Bypassing relays on relay board, the fans start at once.

    Thought it might be temp sensor but then read in Chrysler's official service
    manual that the temp gauge in car gets signal from same sensor. I reason
    that if sensor is off, the guage wouldn't read high either.

    Any ideas?


    P.S. Problem ocurred with two different computers installed. (Replaced for
    other reason.)
    Hank NB, Nov 2, 2005
  2. Hank NB

    Steve Guest

    Are you sure? SOME Chrysler vehicles always used two separate sensors-
    one for the temp guage, and one for the PCM. I own a 3.5L LH car, but
    have never had a coolant sensor problem and so never bothered to check
    in any detail.

    That said, do the fans truly run on low speed when you bypass the low
    speed relay, and high speed when you bypass the high speed relay? The
    reason I ask is because there are failure modes in one of the fan motors
    (the larger of the two) that will cause no fan operation on low speed,
    and either normal operation on high speed or only one fan running on
    high speed (depending on which brush fails in the motor). You should be
    able to see both fans spinning and also hear the difference in pitch
    between low and high speed. The behavior is much like what you get when
    the large fan motor fails and you get no fans at all until the PCM calls
    for high speed fan, then you get reduced fan power.
    Steve, Nov 2, 2005
  3. Hank NB

    Hank NB Guest

    Thank you Steve,

    I did check the fan operation at both speeds, by-passing the relays and both
    fans perform as they should. According to the FSM the temp sensor signal
    going to the computer (PCM) directs both the fan control and the temp guage.
    Also I could tell that when the fans did kick in, it was through the
    low-speed relay because I had my finger on it and could feel it click.

    Have done a little more research and found an old post (Aug 2003), via
    Google newsgroups, on this same group that suggests there are three more
    sensors to consider. They are: Intake air temperature sensor; Output speed
    sensor (not sure what that means); and Transmission oil teperature sensor.
    I'll have to dig back into my FSM (Factory Service Manual) to see if I can
    find anything on those and also where they are located.

    Looking forward to any further input from you folks out there. :eek:)

    Hank NB, Nov 3, 2005
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.