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saa004 February 8th, 2009 17:30

Temperature Light Blinks
When I start my 2004 TDI Jetta GLS and its cold outside, the temp light blinks after the engine has run a few run minutes and remains blinking. The Manual says the fluid is either low or too high. The fluid level is within the requirements (between low and high). Don't understand whats going on there. I'll turn the ignition off and start the engine again and the temp light doesn't come on on again. Does anyone have any recommendations here?


lovemybug February 9th, 2009 01:45

I had the coolant idiot light blinking on my car and it turned out to be the coolant temp sensor. I think it's a similar part on the PD's but don't quote me on that. IMO, that's where I'd look.

saa004 February 9th, 2009 03:14

Sorry, I'm not sure what you meant by IMO. And where is the temp sensor located. I don't have a maintenance manual.


myke_w February 9th, 2009 06:21

Fluid level sender is integrated into the bottle on your car.

Try filling it to the full mark and see what happens, if it still does the same thing, I'd guess the sender is bad.

JPDiesel February 9th, 2009 08:01

I recently had the same problem. I checked the coolant level in the reservoir, which was fine. Then I talked to JASONTDI and he suggested that it could be poor contact in the connector to the sensor in the coolant bottle. Cleaning the connections which looked fine, did not help.

Then still suspecting the coolant level sensor, I took a small piece of 3M nylon abrasive pad in a forceps and polished the sensor bars that are visible thru the filler of the coolant bottle.

This fixed the problem. I think there was some invisible surface film on these bars that did not allow the sensor to read the correct value.

lovemybug February 9th, 2009 10:35


Originally Posted by saa004
Sorry, I'm not sure what you meant by IMO. And where is the temp sensor located. I don't have a maintenance manual.


IMO is shorthand for In My Opinion. The coolant temperature sensor is located, at least on my car, on the driver's side of the engine, facing back toward the firewall of the car. You'll see a junction of coolant hoses there, and then something toward the back with an electrical connection going to it. That should be the coolant temp sensor. If you do a search through here, I'm pretty sure there's a procedure somewhere on how to change it. Like I said, that's what I did, and it fixed my problem.

saa004 February 9th, 2009 18:42

Ok, I'm not entirely sure this took care of it but JPDiesel, I filled the reservoir (just a little, it was way above minimum) and took a very small piece of steel wool and needle nose pliers and removed the film from the bars on the coolant level sensor in the reservoir. I started the engine and NO blinking temperature light. But, I will say the temperature outside hasn't been as cold as it was so I should know if this really was the issue when it gets a bit colder. I'll let you know if the temp light blinks again...

Variant TDI February 10th, 2009 09:41

Mine used to do it whenever the temp was below freezing, but has recently been doing it as high as 46 degrees (via scangauge).

I've been frustrated by the typical responses... There's plenty of coolant there. The contacts are strong. It's a good mixture. And my temp gauge is good (again, scangauge).

Re-cycling the ignition once the coolant is above 60 degrees is the easy fix for the light, but it confuses the hell out of the scangauge, so I've just been leaving it alone to blink recently.

I am excited to try the scouring pad... It would be nice to have a real solution to this little issue.

lovemybug February 10th, 2009 10:00

The coolant temperature sensor actually sends out two signals. One to the ECM, which is what I believe your scanguage is reading, the other actually goes to the temp guage or temp light, depending on particular model. My dash light would blick also, yet the car would run fine. Since I replaced the coolant temperature sensor, the light has not blinked once since then. I would take a closer look at the coolant temp sensor. Just my opinion, take it for what it's worth.

Variant TDI February 10th, 2009 16:17

I will (thanks for the extra info), provided scouring the coolant probes doesn't work.

We'll know in a few days...

Variant TDI February 16th, 2009 17:46

3 mornings below the dreaded 46 degree threshold, and so far, no light.

JPDiesel March 30th, 2009 15:03

Did this work?
I am bringing this thread back to life because I am curious if my scouring fix worked for anyone else.

Has anyone tried this with success or failure?

rez311 April 2nd, 2009 04:19

Well, if your fluid was below the mininum mark, that would explain why the coolant light kicked off... If you get the coolant idiot light again with fluid levels at normal, it's the coolant sender.

mrGutWrench April 2nd, 2009 09:05


Originally Posted by rez311
Well, if your fluid was below the mininum mark, that would explain why the coolant light kicked off... If you get the coolant idiot light again with fluid levels at normal, it's the coolant sender.

__. Every autumn for the past three, at about the first cold snap, I'd start my car in the morning and the light would flash. Same as OP, if I drove it a mile, switched it off, and then started it again, the light would be gone and would stay off until the next morning.

__. The level in the bottle would always be normal (actually, just closer to full). I'd add 4 oz. of distilled water and the light would go out ... until the next autumn. I tried the "cleaning the contacts thing" -- didn't work (but I was wussy about it because I didn't want to overstress the contact prongs so maybe I just needed to scour harder).

__. As a result of this, my bottle has "ratcheted" up to very close to the MAX full line. But it still did it last autumn. And 4 oz. of distilled water fixed it, again.

SuburbanTDI April 2nd, 2009 09:36

I have the same exact issue with two same year, make and model PD TDI's. One silver, one dk blue. One stick, one auto.

On a cold morning light goes on, and you can drive just a block or so - turn the car off then back on - and the light will go off and remain off.

The indicator is positively correlated to the temperature. Colder days cause an issue, warmer days do not. And it is perfectly consistent, on the coldest days you will always find the light goes on.

With one vehicle I added 1 cup of water even though it appeared that the coolant level was perfect. The light went out and never came back on. Problem solved.

With the other car I have done nothing yet and the light still comes on when cold out. It does seem the dividing line for triggering it is just below freezing, but low twenties and below will always find it triggered.

Interestingly on one of the vehicles the problem began the day after Jasontdi had installed an inline 1500w coolant heater. There were no leaks and the coolant was full, but I had initially thought it was related. This occurred at the start of it's third winter. The second vehicle did not have any issue until this year, its fourth winter (This is also just after Jas, did the 100k timing service on it. :) ) . Here is my original post on the issue:

My guess is that adding even just a few drops of water to the reservoir finds just enough slightly less mucked up wire to complete the circuit and send the full signal out to the light. There's probably a better cleaning aid for the sensor strip than steel wool though ...

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