Temperature Sensors Driving Me Crazy

Discussion in 'General Motoring' started by H.H. Mayo, Apr 5, 2004.

  1. H.H. Mayo

    H.H. Mayo Guest

    I had a problem with the engine over heating on my '94 SL2. I traced
    it to the coolant/fan switch sensor which appeared to be doing
    nothing. I bought an after-market sensor and installed it. After
    starting the engine, the temp light came on steady, and the fan began
    to run immediately. I pulled the sensor again, checked the resistance
    across the pins and got a dead short, (Yes, I was very careful, being
    a trained electronics tech). Presuming it was bad, I went and got
    another one with the exact same results. Bad, too, I presume. I
    checked the connector and got good +5 volts on one socket, and good
    ground on the other socket. So, the PCM seems to be working fine.
    Thinking that I must be the victim of cheap Taiwan parts, I bit the
    bullet and got one from the Saturn dealer, and even asked him to have
    a tech check it, which he claims to have done. This time, I did not
    screw it into the block, but carefully attached the connector and left
    it loose. Started the engine and the SAME D**N symptoms. Yanked the
    sensor, checked it at the pins and again read DEAD SHORT CIRCUIT.
    O.K. says I, I run to my parts box, pull out a 2500 Ohm resistor, and
    a 250 Ohm resistor. These represent the top and bottom of the
    resistance range of the sensor which is supposed to go from around
    5000 Ohms to 200 Ohms in range. I plugged the 2500 Ohm resistor into
    the socket and started the engine. All normal, no fan, richer fuel, no
    idiot light, so the PCM is doing what it's supposed to do. Repeated
    the experiment with the 250 Ohm resistor and sure enough, the fan
    comes on as it should, and no idiot light. So, gentle reader, WHATS
    WRONG????? Can all these sensors be bad? There seems to be nothing
    else left.

    H.H. Mayo, Apr 5, 2004
  2. H.H. Mayo

    Joe Biadasz Guest

    Go to a different autoparts store, And make sure they are gettign the
    correct sensor.. Not one that says it "should" work

    Screw it in and have a go at it..
    Joe Biadasz, Apr 5, 2004
  3. H.H. Mayo

    BANDIT2941 Guest

    Presuming it was bad, I went and got
    Did you check any of the sensors for resistance before you put them in the car?
    BANDIT2941, Apr 6, 2004
  4. H.H. Mayo

    H.H. Mayo Guest

    If the Saturn dealer doesn't know which one it is, who should? Not
    trying to be a smart a*s, but the one they gave me looked exactly like
    the others.
    H.H. Mayo, Apr 6, 2004
  5. H.H. Mayo

    H.H. Mayo Guest

    Yes, I went to a NAPA store, and checked the one they offered me. Got
    about 2.5 Ohms that went to zero Ohms. The sensor should be robust
    enough that it can handle the miniscule amount of current from a
    multimeter. The ECM is not capable of putting out much current either.
    The thought that the ECM was somehow burning them out crossed my mind,
    but I don't see how that's possible. THe only other scenario I can
    imagine is that somehow a bunch of faulty knockoff parts has gotten
    into the system. I don't know how likely that is, but from what I
    hear, it's not impossible these days.

    H.H. Mayo, Apr 6, 2004
  6. H.H. Mayo

    BANDIT2941 Guest

    Yes, I went to a NAPA store, and checked the one they offered me. Got
    Another thought;

    Why don't you try using the IAT(intake air temp) sensor in the place of the
    CTS? Its the exact same sensor and you know the one you have should work.....
    BANDIT2941, Apr 6, 2004
  7. H.H. Mayo

    H.H. Mayo Guest

    Another thought;
    That's a good idea. I know the IAT sensor is good. I'll try that and
    post the results.

    H.H. Mayo, Apr 7, 2004
  8. H.H. Mayo

    H.H. Mayo Guest

    Here's the scoop, folks. THERE ARE SCADS OF BAD SENSORS IN THE
    AFTERMARKET BEING SOLD AS GOOD BEWARE! I went you one better and took
    a trip to the local salvage yard. I relieved three dead Saturns of
    their sensors, both fan switch and air temperature (the same). I took
    them home and checked them all out with a multimeter. All read from
    4300 ohms to 3400 ohms, all except one that read dead short. I put one
    of the good ones in my car and fired up the engine. It worked like a
    champ. On examining the one that was shorted, I noticed that the
    construction of it was identical to the two bad ones I bought at
    Autozone, and the one from a local Saturn dealer. That was the one
    that the tech supposedly checked. The good sensors have a deep
    depression in the plastic between the pins located at the bottom of
    the socket well. The bad ones have none, and simply stick up from the
    flat bottom of the socket well. My suspicion is that these are
    counterfit parts, or a huge run of bad ones from the manufacturer.

    H.H. Mayo, Apr 11, 2004
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.