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just changed the coolant temp sensor on 1.9tdi. a quick how to while its still fresh.

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by Jason-Con, Feb 14, 2010.

  1. Jason-Con
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    Jason-Con Member

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    [Feb 14, 2010]
    Maybe this is the wrong place to post this so please do move it to where it belongs if needed.


    Ok well i had the dreaded temp sensor issue where the gauge showed running at 50 or 70, never 90. Now i was told i had a faulty waterpump a while ago by a muppet, even though i proved him wrong in the back of my mind i always wanted to resolve issue with the temp sensor.

    What you will need:

    Green temp sensor with new seal and new clip.
    10mm socket
    Flat head screw driver
    G12 and water to top up.
    Thick skin.....


    Right step 1

    Take the dip stick out and then remove the engine cover with a 10 mm socket.

    Step 2

    Unclip bost hose on the upper top left side and pull to one side.

    Step 3

    Locate the temp sensor, on the 1.9 tdi its just under the bost hose on theleft hand side of the engine, it will have 4 wires on a connector on the back of it.

    Step 4

    Remove expansion tank cap.

    Step 5

    Remove the sender connector from the sensor. Not as easy as it sounds, My first attempt to do this was a total failure and it took me nearly 1 month to re attempt. The connector is on pretty tight to say the least, it will come off but the angels you have to work with are not the best so here is how i did it. I turned the sensor so the i can see the clip part of the connector then with a flat head screwdriver put it in the tiny gap on the clip an slowly tuen to relase the connector. It may of just been mine but for some reason the connector would not budge if i was to pressed the clip section on the connecor, hence the use of a screw driver.

    Step 6

    Again with a screwdriver slowly prise out the securing black clip that holds the sensor in the engine.

    Step 7

    With the connector out of the way remove the sensor from the engine. Coolant will flow out, i did not see the point trying to quickly plugging the hole but you can if you want. I just wanted to make sure i got the job done right. Once the coolant is out locate the seal thich should be in the hole on the engine, then remove it.

    Step 8

    Fit the seal to your new green sensor and insert it,fit the new locking clip and attach the connector.

    Step 9

    Top up you coolant with g12 and water if needed(trust me you will need to later) refit everything else. and run the engine while checking for leaks.

    Step 10

    Once you are happy you have no leaks take the car for a little drive to check the sensor works as it should, it took me about 8-9 mins of driving to get the gauge to read 90. Keep an eye on the gauge as mine did dip for a bit then returned to 90.

    Get the car back home and check coolant level again. I had to top up again as i created a small airlock.
    , hense the slight dip in temp on my short run.

    Hey presto Job done. I would say dont rush,stay calm and tripple check everything.
    Last edited: Feb 14, 2010
    #1
    DieselJake likes this.
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  3. quattrojames
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    quattrojames Moderator Staff Member Moderator

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    [Feb 14, 2010]
    There's another one HERE to accompany yours ;)
    #2
  4. Jason-Con
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    Jason-Con Member

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    [Feb 14, 2010]
    And he has pics too......but the Disclaimer worried me, should i of done one too?:)
    Last edited: Feb 14, 2010
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  5. Quackers
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    Quackers New Member

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    [Feb 15, 2010]
    Having this exact problem! Was going to go and buy a thermostat today, just as well I saw this!

    Looks like that external guide is for 20VT, as its american and they didn't have 1.9TDIs over there, just the 2.7s.

    Going to have a crack at this later, will post pictures if pos.
    #4
  6. crazy88
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    crazy88 Loving the anonymity

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    [Feb 15, 2010]
    Brilliant guide dude, very clear! I really need to get this done on mine, it rarely sits at 90, and does occassionally fluctuate too.

    I have often wondered if this is why my fuel consumption is so random. Sometimes i get over 50mpg, other times early 40s...and that's with similar driving, temperature outside etc. My thinking was that if the sensor is crapped out, and reading low, the ECU will think the engine is cold, so will be using more fuel to compensate? I may be wrong, but thories are always fun!
    #5
  7. Jason-Con
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    Jason-Con Member

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    [Feb 15, 2010]
    Im not sure the sensor will give better mpg if replaced with a new one, if it does then all well and good. I did my drive to work today and still managed the 56.5 mpg that i usually get.
    #6
  8. Quackers
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    Quackers New Member

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    [Feb 15, 2010]
    That would make perfect sense to me! The sensor not only sends info to the temp gauge, but also the ECU. ECU is trying to maintain the perfect AF ratio, so if it thinks the engine is colder than it is, its going to be injecting more fuel. Also on petrol engines, this could cause it to run worse still, as it'll probably be moving the ignition point back in the combustion cycle too?

    Still haven't found my way to Audi just yet...
    #7
  9. Jason-Con
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    Jason-Con Member

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    [Feb 15, 2010]

    When you put it like that i can see your point.
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  10. Garfie
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    Garfie Member

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    [Feb 16, 2010]
    Mine suffered from mpg down in the low 40's and I changed the maf which made no difference to economy but did to performance. Then I tried the coolant temp sensor which made no difference at all, then eventually changed the thermostat which sorted the economy issue. I now get 100 miles more to a tank of diesel with mpg's up to 48-50mpg.
    #9
  11. chrisash32
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    chrisash32 Member

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    [Feb 16, 2010]
    i have changed my CTS as my gauge was all over the place... but now my MPG is awful! I rarely see 30mpg at the moment!! i was seeing 50+ constantly when i first got the car 3 months ago.
    I am tempted to change the thermostat, as it takes AGES to warm up some days... but don't quite fancy doing it myself :(
    #10
  12. jay786
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    jay786 Member

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    [Apr 10, 2012]
    can anyone show me the picture of the location of the temp sensor on a 1.9 tdi .. i have changed the wrong one??
    THanks
    #11
  13. quattrojames
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    quattrojames Moderator Staff Member Moderator

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  14. Gstar51
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    Gstar51 Member

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    [Apr 10, 2012]
    Yeah was wondering why mine never gets to 90 deg, ave to get 1 sorted.
    #13
  15. Gstar51
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    Gstar51 Member

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    [Apr 21, 2012]
    Just changed my temp sensor and made no difference to the temp gauge. Any ideas people?
    #14
  16. stu_m
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    stu_m Well-Known Member VCDS Map User

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  17. Gstar51
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    Gstar51 Member

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    [Apr 21, 2012]
    Cheers stu!
    #16
  18. Johnboymason
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    Johnboymason Member

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    [Nov 23, 2012]
    my car is only doing 38mpg and loosing power every now and then with these codes

    Coolant temp sensor p1256
    Charge pressure control p1557
    so gonna tackle the sencor

    and my temp never goes past 50 :s
    Last edited: Nov 23, 2012
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  19. SL11CKK
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    SL11CKK Active Member

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    [Dec 1, 2012]

    LOL :laugh:
    #18
  20. pauldazzle
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    pauldazzle Active Member

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    [Dec 2, 2012]
    P1256 Change the CTS with a genuine VAG part.
    P1557 looks like you have sticking turbo vanes.
    Low temp is probably a stuck open thermostat.
    #19
  21. tbs
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    tbs Member

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    [Dec 19, 2012]
    Im changing my temp sensor on 2003 1.9 tdi.........see picture below ......can you confirm I can safely remove the big hose arrowed to gain access to the area below that....is that the correct sensor to replace. I took that insert pic by sticking my phone down in the gloom. it looks a really hard spot to get to but i just want to check i've got the right sensor.
    [​IMG]
    #20
  22. stu_m
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    stu_m Well-Known Member VCDS Map User

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    [Dec 19, 2012]
    yeah its safe to remove its the air intake you may get a drop of oil in it but dont worry its normal

    and yes thats the sensor
    #21
  23. tbs
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    tbs Member

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    [Dec 19, 2012]
    Thanks that was a quick reply. Will having the engine warm or cold make a lot of difference to the coolant loss. How much will come out of the sensor hole roughly?
    #22
  24. stu_m
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    stu_m Well-Known Member VCDS Map User

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    [Dec 19, 2012]
    the only difference it will make is it will heat your hands up lol

    you loose about a litre or so
    #23
  25. Paul_TDi
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    Paul_TDi Member

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    [Oct 28, 2013]
    Well I was going to get my thermostat changed but will give the temp sender a go first.

    Just a heads up, if you manage to pull out the old sensor with o ring and have the new sensor with o ring lined up ready to go in you get minimal fluid loss and have no need to top up. I think I stuck in thumb in inbetween sensors as my oring got stuck.

    I replaced the sensor on my 1.9 A3 last year this way.
    #24
  26. Ian2012
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    Ian2012 Active Member

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    [Oct 28, 2013]
    When i changed the sensor on my 1.8t i undid the coolant cap and then screwed it back on, lost no coolant at all
    #25
  27. Paul_TDi
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    Paul_TDi Member

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    [Oct 28, 2013]
    Agreed thats what I did, unscrew to let any residue pressure out then replace to complete a suction to slow the flow.
    #26
  28. quiksilver_jake
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    quiksilver_jake New Member

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    [Nov 4, 2013]
    I have the same issue but have replaced my thermostat which seems to help a little but thought I would replace the temp sensor but I purchased the green one from euro car parts but when I have come to look at mine its black? is there any differance? also I only get the sensor not the o ring and the clip as they say they dont do them? Also how do you get in there as there seems no room?

    Thanks

    Its on an 52 reg 1.9 tdi b6 a4
    #27
  29. demus
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    demus Fire in the hole !!

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    [Aug 24, 2014]
    Had problems with mine showing on VagCom as error 17664, intermittent, open or short to plus, but never saw any problem with the temp gauge.
    It gave up at startup once, symptoms were glow plugs on for about 10sec, started at about 1500rpm then settled, plenty of black soot for a few seconds, rad fans running.
    Had noticed the rad fans running more just lately, probably due to it losing the temp sensor..

    Just for info, if anyones having hassles and searching..
    #28
  30. seven7ten
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    seven7ten New Member

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    [Sep 2, 2014]
    Just replaced mine. No hotter than 70.

    I bought the green 4 pin one, buy mines a black pin one so had to re order. Was really hard to get it in, had to push it down very hard to fit clip in above it.

    Went for a drive and no difference. I'm guessing I may need new thermostat then. :-( any other ideas?
    #29

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