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Thread: Temp sensor versus sender

  1. #1
    Join Date
    Oct 2017
    Location
    Ohio
    Posts
    2
    My Cars
    2001 540i 2001 discovery

    [SOLVED] Temp sensor versus sender

    Hello all recently our 2001 540i has at random started blowing out cold air when the heater is on, I've replaced all cooling system parts radiator, fan clutch, water pump, thermostat, belt. This morning in was driving and I looked down and the temp guage was pegged to red so I promptly pulled over. Checked the coolant level completely full the engine wasn't quite warm het I had just left the house. Grabbed my temp guage from tool bag definetly wasn't overheating. Now when I turn the key 2 clicks so all the dash starts working the twno guage immediately goes To Red even now as it's completely cool. The question I cannot find the answer to is which of the 2 sensors is the sender to guage and which is sensor for fan there s a 4 prong in the top of the water pump round and a square I believe 2 prong in the end of the lower hose. I've been searching for over and hour and cannot find a definitive a seer so I know which one to order. Any help appreciated tha is on advance
    Last edited by Tact1c1an; 10-17-2017 at 03:29 PM.

  2. #2
    Join Date
    Sep 2007
    Location
    Rockville MD
    Posts
    853
    My Cars
    01 540i/6 97 328i vert/
    When were the repairs made. Sounds like a short to ground or poor connection if the gauge is pegged at dead cold. Try and reconnect sensors, and make sure completely bleed system.

    HTH

    John

    PS - have the same car
    2001 540i/6 - 144k

    1997 328 ic - 67k
    hardtop

    2008 328i 6spd 88k

    2008 328i 84k auto

    1998 328i sedan 5 speed - 190k RIP
    1995 325i sedan - Hellrot - 124k RIP

  3. #3
    JimLev's Avatar
    JimLev is offline Artifically Aspirated Moderator
    Join Date
    Oct 2006
    Location
    Sundance Mesa, NM
    Posts
    19,817
    My Cars
    00 540/6, '16 Highlander
    Tact1, welcome to the forum.
    The dual temp sensor in the waterpump housing goes to the DME and the cluster gauge.
    If you disconnect the temp sensor connector when the key is on the temp needle will peg.
    To fix this you need to disconnect the battery (after the trunk light goes out, 16 min) for a few minutes.

    Blowing cold air after the engine is warmed up is a different problem.....there is air trapped in the heater core. You need to bleed the system. You could also disconnect the top radiator hose and pour more coolant into it until it won't take any more, then quickly reconnect it to the radiator.

    The sensor in the lower hose controls the aux cooling fan speed.
    Last edited by JimLev; 10-17-2017 at 10:51 AM.

  4. #4
    Join Date
    Oct 2017
    Location
    Ohio
    Posts
    2
    My Cars
    2001 540i 2001 discovery
    Quote Originally Posted by JimLev View Post
    Tact1, welcome to the forum.
    The dual temp sensor in the waterpump housing goes to the DME and the cluster gauge.
    If you disconnect the temp sensor connector when the key is on the temp needle will peg.
    To fix this you need to disconnect the battery (after the trunk light goes out, 16 min) for a few minutes.

    Blowing cold air after the engine is warmed up is a different problem.....there is air trapped in the heater core. You need to bleed the system. You could also disconnect the top radiator hose and pour more coolant into it until it won't take any more, then quickly reconnect it to the radiator.

    The sensor in the lower hose controls the aux cooling fan speed.
    Thank you yes that's the info I needed I bled it a while back and that quit it's been starting again gonna have to find where the air is coming in at gonna bleed itbwhrn inger back home. I tried the battery unhook for 10 mins and that worked once I get back home going to rebleed check all grounds and battery voltage I normally figure things out myself but For their I'd me I couldn't find which of those 2 sensors down what again ty

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