coolant sensor changed still get intermittent red flashing coolant light

jsweatte

Member
Joined
Feb 6, 2008
Location
North Carolina
TDI
2006 New Beetle TDI
2006 NB TDI, 60k miles, no modifications whatsoever. Car starts and runs normally.
Climate - Eastern North Carolina, warm and humid.
About 2 months ago I started getting occasional flashing red temperature light after driving 2-4 miles. No apparent pattern of occurrence. Temperatures were very warm day/night. Only once did it flash after the car had been driven any distance, when it flashed/beeped then stopped. A check of the coolant reservoir shows good levels but not all the way to the top. I added approx. 1 cup of distilled water. Light stops for a few weeks. I bought a new green sensor from vw dealer as this forum indicates its only a matter of time with the black sensor. This past sunday I changed the sensor and due to the tremendous advice on this site, using the quick replace method, everything went smoothly. I did add some dielectric paste to the electrical connections before replacing. The replacement was done on sunday. Monday and tuesday no issues. Wednesday evening after driving less than 4 miles the red blinking, beeping warning light goes on again. Stops and does not reoccur during the rest of the trip (short duration). Coolant levels are fine, I added approx 1 1/2 cups of distilled water on sunday due to sensor change so resevoir levels are good. Based on what I've seen on this forum the next best guess is the resevoir being at fault or the probes. I will try the probe scrubbing remedy next. Any further advice/thoughts appreciated.

Thanks to all who contribute to this wonderful resource.
 

jcrews

Top Post Dawg
Joined
Jul 28, 2007
Location
Round Rock, TX - VCDS
TDI
All gone
Do you see coolant returning to the bottle? I presume the needle goes to the right, and if it does, the coolant pump might be shot. The plastic impeller can break.
 

jsweatte

Member
Joined
Feb 6, 2008
Location
North Carolina
TDI
2006 New Beetle TDI
Didn't Notice

I'll check that out. I've always had the car turned off when looking at the reservoir, I assume I'll need to have it running to confirm.

Thanks so much.
 

mrGutWrench

Top Post Dawg
Joined
Aug 29, 2002
Location
Carrboro, NC
TDI
'03 Jetta Wagon, 5-speed, 563K Miles (July '23)
__. Mine flashes, indicating "overheat" about every third startup when the engine is overnight cold. If I drive a quarter of a mile, switch the engine off and then start again, the light is out - no more beeping. "Qvality Chermin Mangufatchur"!!!!
 

jcrews

Top Post Dawg
Joined
Jul 28, 2007
Location
Round Rock, TX - VCDS
TDI
All gone
Off of memory, the device resistance is directly proportional to temperature. Have you tried WD40 or deoxit on the ECT connection?
 

jsweatte

Member
Joined
Feb 6, 2008
Location
North Carolina
TDI
2006 New Beetle TDI
ECT connection?

Sorry I'm not entirely sure what the ECT connection is. I'm guessing it's the one I disconnected from the old sensor and put on the new. The only thing I did was put some dielectric grease on both ends and plugged it back together.
 

thatvwguy

Veteran Member
Joined
May 1, 2006
Location
Seguin, Texas
TDI
2004 Jetta TDI & 2006 New Beetle TDI
Wow, deja vu! The symptoms above sound very similar to what I have been experiencing with my with '06 NB TDI.

About a month ago the red coolant light would come on after just a few miles of driving - sometimes solid and some times flashing. This was usually preceded by the A/C shutting off (fan blows but the air is no longer cold) then about 30 seconds later the red thermometer light comes on.

Took it to a trustworthy local mechanic and they said the water pump was okay so it was probably the sensor. Okay to drive as is but need to change the sensor. I swapped out the temp sensor last night and it is still doing the same thing this morning. The reservoir is full. Any ideas?
 

bluesmoker

Veteran Member
Joined
Jun 7, 2006
Location
Maple Ridge, B.C.
TDI
2004 pd 5 speed tip
thatvwguy said:
Wow, deja vu! The symptoms above sound very similar to what I have been experiencing with my with '06 NB TDI.

About a month ago the red coolant light would come on after just a few miles of driving - sometimes solid and some times flashing. This was usually preceded by the A/C shutting off (fan blows but the air is no longer cold) then about 30 seconds later the red thermometer light comes on.

Took it to a trustworthy local mechanic and they said the water pump was okay so it was probably the sensor. Okay to drive as is but need to change the sensor. I swapped out the temp sensor last night and it is still doing the same thing this morning. The reservoir is full. Any ideas?
you have to use vag com or similar to clear the code otherwise it should go away in about 30-40 start cycles
 

thatvwguy

Veteran Member
Joined
May 1, 2006
Location
Seguin, Texas
TDI
2004 Jetta TDI & 2006 New Beetle TDI
bluesmoker said:
you have to use vag com or similar to clear the code otherwise it should go away in about 30-40 start cycles
I never got a CEL and the temp light doesn't come on at start up...it takes about five or six miles. Given that is it still the uncleared code? Is the shutting down of the A/C related?
 
Last edited:

uhhello

Active member
Joined
May 17, 2007
Location
Norwich, England
TDI
2006 Jetta
Sorry to drag this back but I am having the same issues. Light came on about a month ago when wife was driving it home. Came on about 5 miles down the road after the car had been sitting all afternoon. Coolant levels were spot on and all the cars systems work fine with the temp gauge never getting past 150. Drove it the next day with no light or problems. Drove it on a trip to gatwick (2.5 hours) with no lights or problems. Have been driving it for about 2 weeks with no problems but now today we start up and the light comes on before we even move. AC and everything else worked fine along with good engine temp the whole way home. Our European warranty is done but when we move back to the states we will have 1 year left so I would rather not spend money I don't have to. In my warped mind if there is no temp problem and the coolant is good, it can't be harming the car can it?
 

thatvwguy

Veteran Member
Joined
May 1, 2006
Location
Seguin, Texas
TDI
2004 Jetta TDI & 2006 New Beetle TDI
My problem ended up being the water pump. I was at 89K miles +/- so I did the 100K mile timing belt & water pump replacement.
 

DanG144

Top Post Dawg
Joined
Aug 2, 2007
Location
Chapin, South Carolina, USA
TDI
2005 A4 Jetta 5spd
thatvwguy said:
I never got a CEL and the temp light doesn't come on at start up...it takes about five or six miles. Given that is it still the uncleared code? Is the shutting down of the A/C related?
I guess you know by now that the shutting down of the A/C was related. When the ECU sees an overheat condition it shuts off the A/C compressor.
 

acmercg

Veteran Member
Joined
Oct 22, 2003
Location
Lost in CT
TDI
2014 Passat TDI SE 6MT
uhhello said:
Sorry to drag this back but I am having the same issues. Light came on about a month ago when wife was driving it home. Came on about 5 miles down the road after the car had been sitting all afternoon. Coolant levels were spot on and all the cars systems work fine with the temp gauge never getting past 150. Drove it the next day with no light or problems. Drove it on a trip to gatwick (2.5 hours) with no lights or problems. Have been driving it for about 2 weeks with no problems but now today we start up and the light comes on before we even move. AC and everything else worked fine along with good engine temp the whole way home. Our European warranty is done but when we move back to the states we will have 1 year left so I would rather not spend money I don't have to. In my warped mind if there is no temp problem and the coolant is good, it can't be harming the car can it?
I have this exact problem, and I have been driving it over a month like this. The light comes on for me sometimes before I get out of the driveway, but usually it comes on in the first mile. I checked the levels and I Logged it on the way to work one day,
+-65mi, and the water temp never got above 90*c, with an 80*f ambient, and all accessories on, including A/c. There is no code via Vag Com for this and therefore, nothing to reset. I have replaced the coolant temp sensor with the green one, and tonight I will replace the coolant tank. Report back later.

joe
 

OhioDubs

Well-known member
Joined
Dec 3, 2008
Location
Ohio
TDI
03 Golf 10 Golf (RIP)
Faulty coolant bottle. Replaced mine and never had the issue again.
 

acmercg

Veteran Member
Joined
Oct 22, 2003
Location
Lost in CT
TDI
2014 Passat TDI SE 6MT
OhioDubs said:
Faulty coolant bottle. Replaced mine and never had the issue again.
Instantly?

Well, just replaced the bottle, and the light came back as usual, 10 or so seconds after a cold startup... on another note, my Washer fluid light has also been on for a couple of days, figured I'd top it off at the same time, only to find it half full. Topping that off as well did not shut the WW light off either... TIme to pour over the wiring diagrams, maybe they have a common ground or something....
 

OhioDubs

Well-known member
Joined
Dec 3, 2008
Location
Ohio
TDI
03 Golf 10 Golf (RIP)
Yeah mine luckily disappeared instantly. Coolant migration or cluster issues then?
 

turbocharged798

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Joined
May 21, 2009
Location
Ellenville, NY
TDI
99.5 black ALH Jetta;09 Gasser Jetta
I dunno on the MKV's, but on the MKIV's, that is an low coolant alarm, NOT an overheat alarm. It's tied directly to the level sensor on the coolant bottle.

I replaced the coolant bottle and havn't had the problem since. The probes in the old bottle were badly rusted.

A new bottle was under $20 from tdiparts.

Money well spend not to mention it looks great to have a brand new coolant bottle under the hood.:D
 

DanG144

Top Post Dawg
Joined
Aug 2, 2007
Location
Chapin, South Carolina, USA
TDI
2005 A4 Jetta 5spd
Instead of poring over the drawings, just start looking for bad wires. Pull them out of the split loom and look at them.

It probably will not take long to find.
 

acmercg

Veteran Member
Joined
Oct 22, 2003
Location
Lost in CT
TDI
2014 Passat TDI SE 6MT
turbocharged798 said:
Money well spend not to mention it looks great to have a brand new coolant bottle under the hood.:D
I guess this is a plus... matches my newer 5.5l washer bottle. Anyone want to buy a washer bottle with perfect patina?
 
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