Coolant temperature sensor dead! (panic)

[gewstarr]

Hi guys!

I recently bought this '03 Fabia Combi Comfort, which I'm really happy with. However, a couple of days ago the yellow engine light was lit. After driving for a while and then rebooting the car the light was gone. Fine. However, now it's back, and this time it just won't go off. I have bought a cheap OBD2 interface (KL/KKL) that I should be able to hook up with my ASUS Eee using VCDS-Lite or something. Anyways, I'm having some issues with getting the software to work in my Windoze 7 environment.

However, this very evening I suddenly noticed something that got me less thinking about any possible fault code that could be turning up the light. It was all suddenly very clear to me. The temperature was not showing anything. It was stiff at the left you know, nothing, zero, squat. Felt really insecure to be driving around, and besides, I don't know what the temperature reading does except for telling the driver the current temperature, i.e. if it's surpassing it's data to other vital components of the car system.

I was search around, and found tons of threads on this very forum. I have the 16v/75hp engine, and I finally managed to pull the plastic cover over the engine away so that I could see what's under. I found some stuff that felt like it could be the coolant sensors. I tried pulling in the thing to the right (on my attached photo), but it wouldn't move, and I did not have any tools with me a the time, not even a small screwdriver to unclip it.

Later, I went back home and searched the net. After running the digits that can be seen (if you zoom in) on the thing, it doesn't seem to be the temp sensor, but some sort of exhaust gas valve, in other words not what I should be looking at. Now, I was thinking that perhaps that green thing to the left (also in my attached photo) is the real deal. So, I just wonder if anyone here could tell? I'm a real newbie when it comes to this machinery.

Also, is there anything special I should think about? Furthermore, this seems like a somewhat common issue, is it?

Thank you guys in advance, you've been much helpful here before.

Cheers!

[sepulchrave]

Yes it's common and yes, it's the blue/green thing on the left, the other thing is indeed the EGR valve which also goes wrong a lot.

 

Go buy a new one, drain the coolant from the tap under the nearside front of the car into a washing up bowl, swap them over, refill the coolant, done.

[Breezy_Pete]

Follow the radiator top hose back to the engine, and you should see a plastic fitting like on this page. Coolant temp sensor is item 18, right next to where the top hose attaches.  Green thing in your pic is oil pressure switch I think.

[gewstarr]

Big thanks for your help, guys!

 

This evening I went ahead and made another effort, and now I may be in some trouble. I had a difficult time finding the sensor, but finally I saw it. Unfortuantely, they have placed it in a place where it's really tight to reach in with your hands. I was rushed, and just wanted to see how the damn thing looked. Without thinking, I popped the C-clip and pulled the thing. Guess what happened? Correct, red liquid started pouring out in the engine compartment. I paniced and tried pushing the plug back in. It was really hard, mostly because of the O-ring that gave some counterpressure, and getting the clip back on was really hard. Finally, we had a small river under the car on our parking lot, but the sensor and clip is now back on it's place. The coolant level is now at the minimum level in the can, so not _all_ the coolant have leaked out, anyways.

 

So, I started the car, just to see if there had been some simple oxide/connection issue that would now be solved by all tweaking with the sensor. Now, after only seconds the engine started sounding really nasty. It was really vibrant, and I felt a weird smell. I turned it off, really scared that I am _this_ close to having a major engine collapse. I'm not sure what may or may not have happened. Do you guys have any idea? If I leave it over night, will things be different if I try to start it tomorrow, when most coolant must have dried. What do you guys think? Any other ideas? Right now I'm really scared.

 

[ajs_vrs]

The coolant temperature is obviously to see what the coolant temperature is.

It's also used in the ECU to determine how much fuel to inject and is referenced in various tables (without going into too much jargon/unnecessary detail..

Upon cold start up it is referenced and the car determines how much fuel to inject and how high in rev's to idle (at the point the o2 sensor is ignored), some cars have a air pump to heat up the CAT (purely for emission and typically engaged for around 30 seconds or so) and this is disabled/enabled dependent on coolant temperature.

So the ECU determines how high it should idle and how much fuel to inject since its basically like the old manual choke back in the day.

You could check what it reads with an OBD2 reader but its likely nothing and thus the car wont have a clue what to do its either very high or low.

RE leaving it, depends what its state was when you tried to start it up. You dont want too little coolant since it cools the block however IMO you have likely not caused any damage it it was only started/ran for a short period of time. Coolant will smell too.

If it was me, I'd leave it get a new sensor and try and jack the car up fit the new sensor then replace with some coolant, however depending on the amount leaked it may have air in it which will effect how the car runs because it will likely have a fluctuating a temperature. The easiest method to bleed is follow the bleeding procedure ie bleed nipple etc,

OR

Jack the front of the car up high with rad cap off and let the bubbles comes out (when hot) the level will jump up and down or put a transparent pipe over the bleed nipple take rad cap off and blow into it with engine off, you should after a short while see bubbles come out of the pipe. Both methods work work well when car is fully warmed up/engine off fully warmed up.

Or if you want to risk it, top it up, drive to nearest garage with the sensor you have bought and get them to fit the sensor and bleed the system - though I'd keep on the look out for any leaks.

[gewstarr]

@ajs_vrs: Big thanks for your detailed explanation, much appreciated. I was actually asking myself that (about the temperature sensor <-> ECU relationship) just the other day. More precise, at first I thought that the broken temperature sensor was no big hurry, i.e. it could wait at least a couple of weeks or so, because it's only function was to show the operating temperature in the display panel, and if the car would become overheated I guess I would see some smoke or other visual/hearable signs anyways.

 

But then, I laid flat on my bed and thought that it actually made sense that the sensor would serve other purposes, for instance telling the ECU when to activate the big fan in the front. Then, I suddenly got more interested in fixing the problem right away. Now, back to the issue that has become out of this stupid rash of mine, i.e. pulling the plug without first draining the coolant system. Well, just an hour ago I went out and started the engine again. The vibrations in the coupe was sincere; it was not just my imagination. I went out and popped the hood.

 

Wow. The engine was literally bouncing. I have never seen anything like this. I took my phone and captured some video. Guys, what are your thoughts on this?

 

http://www.youtu.be/rJIi3Xpd5CE

 

Oh, I've now ordered a new temperature sensor, it'll be here in 1~2 days, hopefully.

Edited 8 September, 2013 by gewstarr

[chrisw880]

Wow. The engine was literally bouncing. I have never seen anything like this. I took my phone and captured some video. Guys, what are your thoughts on this?

 

http://www.youtu.be/rJIi3Xpd5CE

 

Oh, I've now ordered a new temperature sensor, it'll be here in 1~2 days, hopefully.

 

Could be wrong, but it sounds like its running on 3 cylinders 

[Breezy_Pete]

^ I'd agree (maybe even fewer!).  This may be consistent with really inaccurate fuelling caused by the temperature sensor giving wildly inaccurate info to the ECU. Check the wiring to the sensor connector isn't bust, and the contacts aren't corroded before you re-connect it too.

 

Replace the sensor, using the method suggested by sepulchrave, above.  Don't run the engine any more until it has the new sensor, and a full complement of coolant in it.

[gewstarr]

Thanks for all your help guys. I managed to mount the new temperature sensor today, as it arrived by mail. In fact, first I snapped the plastic clip so I had to bicycle >5 kilometres (x2; back and forth you know) to our local certified Skoda garage to buy a new one. Good music filled my earphones, so the trip was good though. Anyways, cylinder misfire issue consisted after I had changed the sensor. I changed all four spark plugs, but the machine still sounded like a tractor. Finally, I took use of the fact that VCDS Lite always complained about the first cylinder in line. I changed the coil for a brand new one (cheap third party, though) there, and the car suddenly worked a charm.

Cheers!

[ajs_vrs]

A coilpack will cause the spark plug to not ignite,in future you run the engine and take each pack out if the noise of the engine alters the pack is fine if not the pack is faulty.

 

Glad to hear its running ok again.