Coolant Temp Sensor Replacement

Greentone

New member
Joined
Aug 13, 2006
My coolant sensor needs to be replaced in my 04'Jetta. Instead of paying 140.00 to get it installed I purchased one from the dealer for $30.00 and hope to install it myself. This website has been a help in the past but I can't find any instructions on how to replace the coolant sensor. It's to dark out to look under the hood today but I'll be attempting to do this tomorrow. I'm looking for advice, point me in the right direction please I have no idea what I'm doing or where this sensor goes.
 

tkindler

Veteran Member
Joined
Oct 3, 2003
Location
Southwest Louisiana
TDI
Jetta GL, 2003, white
Remove the engine cover and on the driver's end of the engine, look for a part with three plugs sprouting from the top as in this picture:

http://pics.tdiclub.com/showphoto.php?photo=30802&cat=500&ppuser=16933

On the back side toward the bottom of this part is the coolant temperature sensor. It has an electrical connection with a wire coming from the back side of it. It is held in place by a little plastic clip which can be pulled off toward the bottom of the sensor. Be gentle, the clip can break, and if you drop it, have fun looking for it. You will need it to secure the new sensor. Some folks suggest having a replacement available, just in case. The steps I followed when I replaced mine are as follows:

0. It is best to do this while the engine is cold.
1. Open the top of the coolant overflow container to relieve pressure.
1a. You will probably want to remove the large hose running from the airbox to engine. This will make access to the sensor easier.
2. Remove the electrical connection from the old sensor
3. Connect electrical connection to the new sensor, so if I drop it, it doesn't get lost.
4. Remove the retaining clip holding the sensor in place
5. Be sure you have the new rubber O-ring on the new sensor
5a.Remove the old sensor, being prepared for coolant to come out.
5b.Pull and twist the sensor, it should come out fairly easily.
5c.Check to be sure the rubber O-Ring came out with the old sensor
6. Quickly insert the new sensor with the new O-ring to prevent coolant from leaking
7. Re-attach the plastic clip to secure the sensor.
8. Check coolant level and, if necessary, top up with the recommended mixture of G12 coolant and distilled water. I used 50/50, although I don't think that is the exact recommendation. If you don't have G12 coolant use distilled water only.
9. Put top back on coolant overflow container.
10 Re-attach any other parts you removed.

Note: Yours is a PD engine, mine is an ALH, but I think all this applies to your engine. Someone else chime in if I am mistaken.
 
Last edited:

whitedog

Veteran Member
Joined
Jul 12, 2004
Location
Bend, Oregon
TDI
2004 Jetta that I fill by myself
tk, I have two questions.

One is do you twist the sensor because that is part of the lock or is that just to break it loose?

Secondly, can you pull out the old sensor enough to see the o-ring is on before the coolant starts to flow?
 

paramedick

TDIClub Enthusiast, Vendor
Joined
Jul 29, 2001
Location
Versailles, Kentucky
TDI
2015 Audi Q5 TDI
Well, I ain't that fast (old and slow) and invariably the O ring doesn't come out, so I use an alternate method.

I use an 18 inch piece of clear tubing of the appropriate size. Clean the drain nipple, attach tubing and route to empty gallon milk jug. Open the drain and fill the jug. Close drain, pull the tubing, and cap the jug.

Now change your temp sensor at your leisure. No spillage. Pour the coolant back in.
 

tkindler

Veteran Member
Joined
Oct 3, 2003
Location
Southwest Louisiana
TDI
Jetta GL, 2003, white
WD - Once the clip is removed there is no other locking mechanism. I just jiggled and twisted a bit to break it loose.

I didn't really take time to check. Since the cooland was cold and not under pressure, I didn't loose much anyway.

Paramedick - I like your approach. No need to rush.
 

JayT

Veteran Member
Joined
Dec 11, 2004
Location
Pennsylvania
TDI
Golf, 2003, Silver Beetle, 2013, Moonrock
my two cents since I too read on here how to change sensor. I'd go for an alternative to pulling out the sensor and then putting the new one in. The new one did not go in so easy and I lost alot of fluid then I had to go to VW and get some g12 coolant, which they only had in gallon size, so cost me an extra 20 for repair.

Having said that, its awesome that this forum is around to help up defer some cost by doing work ourselves.

jt:cool:
 

Greentone

New member
Joined
Aug 13, 2006
Thanks for all the info everybody. Got the sensor switched today and my car is running better than ever.My engine was getting flooded because of the bad sensor. Not any more!
 

REBEL TDI

Member
Joined
Nov 15, 2005
Greentone said:
Thanks for all the info everybody. Got the sensor switched today and my car is running better than ever.My engine was getting flooded because of the bad sensor. Not any more!
Just out of morbid curiosity, how long did it take you? I'm kind of slow myself when I work on the car. That's a project I have scheduled for tomorrow as well as replacing the vacuum lines if I can find them this afternoon after work.
 

McBrew

Top Post Dawg
Joined
Oct 30, 2002
Location
Annapolis, MD
TDI
2003 Golf GLS TDI, 5 speed, Silver/Grey
For those who need to do this job, you can often find a new coolant sensor for around $18 at TDIparts.com. I picked up a few at Impex on sale for $5 each.
 

REBEL TDI

Member
Joined
Nov 15, 2005
From the picture you have and looking under the hood of my car; isn't it behind those three plugs in the picture? Like facing the firewall? I haven't had the time to replace mine yet.
 

NutnBolt

Well-known member
Joined
Jul 13, 2006
Location
NJ
TDI
2002 Jetta TDI Manual Black
I attempted doing the quick swap method and although the old black sensor came out quite readily, the new green one was not easily inserted. In my
rush to stop losing fluid, I ended up cutting the o-ring while pushing it in.

Did not realize the o-ring was cut and since there was fluid all over, I did
not notice it was leaking. Took the car for a short spin and just before
pulling in the driveway the coolant light began blinking.

Pulled out the sensor the next morning - had to let it cool - it was hot. I
let the coolant spill slowly into a small yogurt cup placed under the sensor and sucked it up as it filled with a turkey baster into a larger container.
Once it had cooled I pulled out the sensor and saw the damaged o-ring.
Went to dealer this morning and got a new o-ring and some G-12 and
put it back together the right way and filled with 50/50 G-12/Distilled water.

Appears to be fine. If you want to do this and not have to worry about rushing or screwing up, drain some coolant first - either from the drain nipple, or from the sensor.
 

vigog

Member
Joined
May 18, 2003
Location
Yrokville, NY, USA
TDI
2002 Jetta GLS 5spd.
Yes REBEL the sensor is behind and slightly below the plugs.

The job took me about 10 min.

One thing that is helpful is to practice taking the connector off the temp sensor by taking a connector of in a more accessible location such as the MAF sensor which has the same type of connector just bigger.

It is suggested that you wash down the engine if you do spill any coolant

Here is a good how to..... http://www.inmud.co.uk/page27.htm
 

Eudaemonic

Well-known member
Joined
Aug 15, 2005
Location
Boston, MA
TDI
'02 Black TDI Golf
Thanks for the write-up! Nice to read about this as I have to do mine soon.

Quick question though. NutnBolt mentioned something about an old black sensor and a new green one. Is the green one an new/updated version? Someone else told me about it, saying the black one is cheaper. But is the green one better?

Another quick one. I'm used to the old mkIIs. Are there 2 CTS (one for the ECU and one for the instrument cluster like in the good old days, or only one CTS for both?

Thanks
 

EddyKilowatt

Veteran Member
Joined
Mar 1, 2006
Location
Carmel Valley CA
TDI
2003 Golf GL 5M
vigog said:
One thing that is helpful is to practice taking the connector off the temp sensor by taking a connector of in a more accessible location such as the MAF sensor which has the same type of connector just bigger.
That's a great idea. The connectors on these cars are impressively well designed, but they're often smarter than I am... figuring out how to release the latch mechanism -- especially if the connector in question is shoulder-deep in the engine bay -- is often the hardest part of the job. :eek:

Maybe How-To's that include the words "just unplug the XX connector" should include "the XX is similar in style to the YY connector"...

Eddy

p.s. Eudaemonic -- two sensors, one housing.
 

mparker326

Veteran Member
Joined
Feb 28, 2005
Location
Knoxville, TN
TDI
Golf 2002 Gray
Eudaemonic said:
Quick question though. NutnBolt mentioned something about an old black sensor and a new green one. Is the green one an new/updated version?
Yes, the green one replaced the black one. AFAIK, you can only buy Green and Blue sensors. Most cars take the Green and a few older model cars take the Blue.

EddyKilowatt said:
figuring out how to release the latch mechanism -- especially if the connector in question is shoulder-deep in the engine bay -- is often the hardest part of the job. :eek:
That is where mirrors come in handy. Even if you know how to take it off, it is a pain if you can't see it since VW loves to place things upside down.
 
Last edited:

Eudaemonic

Well-known member
Joined
Aug 15, 2005
Location
Boston, MA
TDI
'02 Black TDI Golf
mparker326 said:
Yes, the green one replaced the black one. AFAIK, you can only buy Green and Blue sensors. Most cars take the Green and a few older model cars take the Blue.
Older as in what year/engine code? Mine is a 2002, ALH engine IIRC.

Thanks
 

mparker326

Veteran Member
Joined
Feb 28, 2005
Location
Knoxville, TN
TDI
Golf 2002 Gray
Eudaemonic said:
Older as in what year/engine code? Mine is a 2002, ALH engine IIRC.

Thanks
Chances are it will take the green. The easiest way to tell is to go unplug the electrical connector from your CTS. If it is D shaped, get green. If it is square, blue is in order.

My 2002 Golf took a green.
 

uglide1996

Active member
Joined
Nov 22, 2006
Location
Gardiner, NY 12525 USA
TDI
2002 Golf 5spd, 2002 Jetta 5spd, 2014 Passat DSG
Green replaces black, VW knows black ones are failure prone. The price of these used to be $8.00 but now are $26.00, VW dealer parts guy says this is because VW knew black ones were problem parts and now feels that if your black one worked this long it's just normal parts replacement, I believe this claim because he has never charged me prices out of line with independant parts jobbers and he seems willing to give out accurate advice. I like Paramedick's coolant approach, it's the sensible way to do this, it gives you time to make certain the o-ring is set properly. I suggest getting a spare plastic retainer clip, thing that holds switch against o-ring, I replaced mine Sunday night (never a good thing!) and the clip broke, never happened before, right? So make sure to have a retainer clip too, just in case. Also I got frustrated with the release on the wiring plug so I removed the clip first then removed the switch still attached to the plug (don't forget to remove the old o-ring from the housing!), then installed the new switch, once the old switch was out of the housing I had easier access and visibility to the connection. Now if only I didn't break the retainer!
 

HereToday

Member
Joined
Aug 28, 2004
Location
FL, USA
TDI
Jetta, 2003, Galactic Blue
First, thanks for the great directions on replacing the sensor. I just did mine today and, although I used the drain into jug method, I still lost quite a bit of coolant. It went everywhere but I had an old piece of plastic below the car so I was able to catch it all and keep from too much of a mess.

Unfortunately, I broke the retainer on the wiring connector. I had no issues with the retainer spring clip for the sensor itself. Just for the wiring connector. I rigged it with a piece of wire holding the electrical connector in place but I would love to replace the black shroud over the wiring so that I can rest easy on long trips. Anyone know what the part number is for this particular connector?
 

poor1

Veteran Member
Joined
May 3, 2003
Location
UK
TDI
MK4
Very useful to have pointers when you are not a professional doing these things every day and these are excellent. Bit tricky putting drain hose on the bottom radiator without taking the under pan off, but it can be done by taking a couple of the Torx fastening screws out. Also useful to take the bumper grill out - it is just clipped in and come out easily. The uprated temp sensor part, green colour, is part number 059 919 501A and costs £27.00 Sterling, full VW main dealer retail.
 

Tickbait

Requiescat In Pace
Joined
Oct 6, 2003
Location
None
TDI
None
Been there and done that. The instructions on here take all the guess work out of it.

Start to finish in no time and good ever since.
 

TDImonkey

Well-known member
Joined
Jan 4, 2005
Location
Niskayuna, NY
TDI
VW Golf 99.5 Blue 2Dr
Did this repair today. Very easy once I got the right temp sensor. However, before getting the right one, I did manage to spill plenty of coolant inside the engine bay. Does this burn off on its own harmlessly, or should I hose off the engine?

Also, I couldn't find the old O-ring after pulling the broken temp sensor. May have fallen out on its own, may still be in there. Quick poke with my fingers showed nothing. Will this result in a slow leak or any other problems?

Thanks!
 

Turbosprezarka

Veteran Member
Joined
Feb 1, 2006
Location
New England
TDI
2001 Jetta TDI (ALH) GLS, 5sp, Tornado Red, 301,593 miles, SOLD
About to do this tomorrow actually, as my sensor has been reading these crazy and sporadic measurements lately. So quite ironic I ran into this recent thread.

Kinda hoping this improves cold weather starts a little.

TDImonkey said:
I did manage to spill plenty of coolant inside the engine bay. Does this burn off on its own harmlessly, or should I hose off the engine?
I had coolant dry ona work lamp before, and it left a whitish/pinkish film.
 

TDIRyan

Veteran Member
Joined
Jan 28, 2005
Location
Memphis, TN
TDI
02 Jetta TDI Black
I'm guessing if you have a steep hill with the front passenger side of the engine faced down the hill you wouldn't lose any coolant at all.
 

B100

Veteran Member
Joined
Jan 7, 2003
Location
Berkeley, Eastbania
TDI
2003 Golf
tkindler said:
Remove the engine cover and on the driver's end of the engine, look for a part with three plugs sprouting from the top as in this picture:

http://pics.tdiclub.com/showphoto.php?photo=30802&cat=500&ppuser=16933

On the back side toward the bottom of this part is the coolant temperature sensor. It has an electrical connection with a wire coming from the back side of it. It is held in place by a little plastic clip which can be pulled off toward the bottom of the sensor. Be gentle, the clip can break, and if you drop it, have fun looking for it. You will need it to secure the new sensor. Some folks suggest having a replacement available, just in case. The steps I followed when I replaced mine are as follows:

0. It is best to do this while the engine is cold.
1. Open the top of the coolant overflow container to relieve pressure.
1a. You will probably want to remove the large hose running from the airbox to engine. This will make access to the sensor easier.
2. Remove the electrical connection from the old sensor
3. Connect electrical connection to the new sensor, so if I drop it, it doesn't get lost.
4. Remove the retaining clip holding the sensor in place
5. Be sure you have the new rubber O-ring on the new sensor
5a.Remove the old sensor, being prepared for coolant to come out.
5b.Pull and twist the sensor, it should come out fairly easily.
5c.Check to be sure the rubber O-Ring came out with the old sensor
6. Quickly insert the new sensor with the new O-ring to prevent coolant from leaking
7. Re-attach the plastic clip to secure the sensor.
8. Check coolant level and, if necessary, top up with the recommended mixture of G12 coolant and distilled water. I used 50/50, although I don't think that is the exact recommendation. If you don't have G12 coolant use distilled water only.
9. Put top back on coolant overflow container.
10 Re-attach any other parts you removed.
Thanks for guiding me along. A few steps I noted today while replacing the old Black sensor with a new Green one:

1. It was also helpful, in addition to removing the air inlet tube, to remove the cover of the air filter, which gave me more elbow room.

2. A sliced-in-half-vertically gallon milk jug was just the ticket to twist into position to capture the escaping coolant. I sliced right through the mouth, which fit nicely below the sensor housing.

3. Almost half a gallon of coolant came out... more than I had expected. Some spillage, good to have rags spread below in the cramped space.

4. I should have supported the milk jug from below, as it got heavy. I was holding it with my hands, and had to yell for my wife to bring a rubber hose that I used siphon out the liquid. I should have been ready to handle the coolant once it was caught in the tub.

5. I replaced the plastic clip from above, seemed safer should I need to get back in there, to pull it up, than to yank it down.

Temp gauge on the dash seems stable now.
 
Last edited:

cerickson

Well-known member
Joined
Aug 15, 2005
Location
Teton Valley, Idaho, Wyoming
TDI
2002 Golf, Silver
Before I did mine I asked Drivbiwire for some advice. Credit and thanks to him for this procedure. I'll try to summarize what he said and describe how I did mine. The basic idea is to drain some coolant from a convenient spot first so nothing comes out when you pull the old sensor. Plus you want it to come out of the engine, not just drain your radiator.

This was on my '02 golf.

I went up on the blocks, removed belly pan and engine cover and air intake hose for better visisbility/access.

Be prepared to catch the better part of a gallon of coolant in a clean container. I pinched off the hose to the oil cooler and since I have a TDI heater installed that is where I unhooked a coolant line to drain into a bucket. After the coolant coming from the TDI heater ran out, I undid the pinched line and collected some more from that side. After draining go ahead and reattach the coolant line to the TDI heater. (if no TDI heater then you're just dealing with the two oil cooler hoses)

Now go find your sensor, unclick the electrical connector, pull down the plastic circlip and out she comes, mine came out with the o-ring neatly.
Put in the new one with new o-ring. Reattach the elec. connector.

Got my green one from TDI parts, Peter was kind enough to put in a new circlip gratis, thanks! (I didn't end up breaking the old one but it was a good feeling to have a new one ready to go)

Now to refill coolant. I filtered through cheesecloth what I caught in the bucket and poured into the reservoir. To the top/right side of the reservoir is the coolant return line. Undo the hose clamp and hook up a vacuum pump to draw coolant from the res into the engine. I refilled the res twice to do this.

Finally, start the car and hold the revs at 2000 for a couple of minutes to purge air from the system.

Criuse down the road and enjoy your new found guage accuracy!

Thanks Drivbi and Peter Noble!!:)

Chris E.
 

NeXTstep guy

Veteran Member
Joined
Jul 30, 2000
Location
Vancouver, BC, CANADA
TDI
Jetta, 2003, Silver
Could someone give me some really, really, really, detailed instructions about how to disconnect the connector? I tried (incorrectly/unsuccessfully) to remove this type of connector on my MAF. It befuddled me. What's the secret?
RWW
EddyKilowatt said:
That's a great idea. The connectors on these cars are impressively well designed, but they're often smarter than I am... figuring out how to release the latch mechanism -- especially if the connector in question is shoulder-deep in the engine bay -- is often the hardest part of the job. :eek:
Maybe How-To's that include the words "just unplug the XX connector" should include "the XX is similar in style to the YY connector"...
Eddy
p.s. Eudaemonic -- two sensors, one housing.
 
Top