Afternoon all, has anyone ever fixed the know big with Skoda Fabia 1.4MPI engine  coolant temp sensor warning. 
It’s my second Fabia (albeit this one is my other half’s) and I’ve been fixing the usual snags, but can’t seem to shift Warning.
We Have had a new rad, temp sensor, coolant housing, (think the thermostat was included) and I’ve taken off and cleaned a couple of the electrical plugs. 
move scanned the car a few times, and although the light comes on without fail, (even when engine is warm) it doesn’t always give a code. 
Thinking of changing the thermostat myself (so I know it’s defiantly been changed) but the temp needle on dash seems to work as advertised. 

You might need to change the coolant reservoir bottle, or check that none of the wires feeding the bottle sensor have been cut (as happened to me)

Thanks for your reply. That’s what I meant by coolant housing (as it has an integral sensor). Haven’t check the wiring though so will have to check that. 

What year is the car?

Earlier Mk1 Fabias seem to suffer a variety of faults associated with the solder joints of connectors on the dash cluster circuitboard, one of which takes the signal from the coolant level sensor in the expansion tank.  If the wiring in the engine bay looks to be intact, it may be worth having a look at these solder joints, looking for cracking around the connector pins.  Coolant level is pin 16 on the left end of the inner row in this pic (but check all the pins while you're at it, and re-flow any that look even slightly dodgy).

 

 

Edited 8 May, 20206 yr by Wino

Thanks for the info. It’s a 2002 model do believe it’s a MK1? Is that PCB on the dash? 

Yes and yes. 

Thank you. I’ll buy myself an AVO to carry out some electrical tests. I’ll look into stripping the dash down, is it a big job? 
min currently using the Give it some mileage as it was sat for a while and don’t have a drive at the moment so not much room to strip car down too much. Fixing faults on the side of a street lol 

The cluster comes out quite easily.  Adjust the steering wheel to its lowest position first. A plastic trim panel  below the clear screen of the cluster just pulls off and reveals a couple of torx screws, remove those and the cluster pulls out towards you.  But not far because of the wiring.

Reach behind and carefully release the two loom connector latches, and connectors, then slide the cluster out from behind the steering wheel.

 

Once you have it out, there are some little plastic ramp catches that hold the rear cover on, release those and the whole innards comes out as one, leaving you with what's shown in my photo.  You can probably see enough with suitable light and magnifying aids to inspect the green connector solder joints without removing all the needles, bezel etc. 

Okay, so it was quicker for me to remove the dash than inspect the wiring loom. (Lockdown and 2 kids, time is of the essence). It was difficult to actually take a good picture of what I saw, but it looks slightly discoloured around a few connections which I think are slight deformations in the solder. (Under a x20 magnifier). 

 

Oh, yes, looking very much like cracked joints from vibration of those pins within the solder. Great pic!  If you try moving the connector, you may even be able to see the pins wiggle within the joints?

 

Reflow the solder round them and expect problems to vanish.  What's the other end of the row like, same?

Edited 11 May, 20206 yr by Wino

Okay so took it to work today. Reflowed the solder and just reinstalled it but still the fault returns. Don’t even have to start the engine. Can just leave ignition on and it comes back, scanned the car and it found no faults. 
Back to the old drawing board as they say. 

Sorry to hear that wasn't a success. Now that you're expert at removing the cluster it should be easier to check the wiring though.  Blue/red wire (from pin 1 at the bottle connector) goes to pin 16 of that green connector, brown/white (from pin 2 at bottle connector) should get to pin 32, next to it.   If you link the pins at the bottle connector (or the green cluster connector) you should be able to measure zero Ohms between the pins at the other end. 

Start with a more thorough visual inspection of the wires heading away from the expansion tank though, that's where damage seems most likely to occur. (Double?)Check that the pins coming out of the tank, and the mating sockets in the loom connector are uncorroded too.

Edited 13 May, 20206 yr by Wino

Okay. So had another quick look after work. Unfortunately my multimeter connectors are too big to carry out the test you suggested. I’ll device some smaller connectors tomorrow and try it out. I couldn’t see anything obvious with the connections though. I’ll add some pics now. 
 

Does wiring from Pic 1 lead to Connector in pic 3 then onto ECU in pic 4. 
And is there a wiring diagram of the cooling system anywhere? 
 

 

 

Picture one is the coolant temperature sensor connector, is it? I haven't referred to that in my descriptions, because I assumed that the problem was the coolant level warning (flashing red LED)? I can look up the wiring route for those wires shortly.

 

What I was describing was the testing of the two wires in picture 2 to their destination at the green cluster connector. There is one intermediate connector behind the wiper motor in the firewall but that connection doesn't usually give trouble.

 

 

Edited 13 May, 20206 yr by Wino

I think your coolant temperature sensor wires go direct to the engine ECU without any intermediate connections.  Blue/red to ECU pin 104, brown/blue to pin 83.

Hi again mate. 
 

yeah the pic is coolant temp sensor. (I don’t believe it’s the sensor for three reasons 1) it’s already been changed, 2) the temperature gauge is behaving (not staying on nothing and then moving) and 3) because there isn’t a hard fault on the code. My previous Skoda Fabia was a 2000 year model and it was a hard fault. 
I just looked at the wiring to try and eliminate that part of circuit and it was easy to follow routing. 
according to the Haynes manual there’s another connector on the circuit between instrument panel and the earth. But that was as far as the diagram went. Didn’t even tell me which earth. Lol 
 

Tomorrow I’ll make some small pin contacts to use in the green plug from instrument panel. Certainly stinks of an electrical fault. 
I will at least be able to test the circuit from the coolant reservoir connector to the instrument panel. 
could just be a dodger earth somewhere. 
The main ones are on top of the battery (i think) and they look in good condition. 

Just remembered an easier test for the level sensor wiring.  Unplug the connector from the expansion bottle and link out the two contacts with a piece of wire. Ignition on or start the engine and see if the warning light now doesn't happen, if so the wiring is OK; if it still does happen, then the wiring, or the cluster circuit is faulty.  Probably worth doing that before continuity testing the wiring, because it effectively does the same (especially if the wiring isn't at fault).

Cluster circuit? 
That test makes sense. Any idea why the two wires? One to dash board, other to ECU? 
I’m assuming all fault codes come from the ECU, As there isn’t always a fault code and just a light/noise, it must be wiring. 
so using that logic, where else in the system could that warning come from? 
 

 

The instrument cluster PCB has the circuit that drives/reads the level sensor probes in the expansion tank. Both wires from the level sensor connector go to that green connector, pins 16 and 32, although the 'sender earth' brown/white one links up with lots of other sensors too. Fault codes can be generated by all the control modules, including the instrument cluster, but many code readers only read the engine ECU, ABS module etc.

What fault code numbers have you seen?

I'll have a look at wiring diagrams again at some point but those all seem unrelated to coolant level or temperature warnings, unless there's a shared earth that isn't working well.

 

You'd need to scan the 'instruments' module to see coolant level fault codes I think, which code readers like that won't do. 

VCDS Lite recommended. Cheap compatible lead converts car diag skt data to usb, then a laptop with free-to-download software from Ross-tech interprets it.

Okay mate. Cheers. 
is that an app or a handheld device? 
 

VCDS Lite is a program that runs on windows computers. It only works with third-party cables (not supplied by Ross-tech).  These cables vary in cost from about a fiver to about £20.

I think what you have screenshotted is the 'full' VCDS program, which is free to download, but only works with cables supplied by Ross-tech, at significant cost.

Go here and you can read about all the options: https://www.ross-tech.com/

VCDS Lite only works with older VW-group cars, up to around 2004, but all Mk1 Fabias work with it.

 

Okily dokily. Good old amazon prime. Purchased a cable and will download app later. 
will run some tests and report findings in here tomorrow. 
 

thanks for your assistance.