Hi all, lust joined here. Im a trader and specialise in VAG cars. I have genuine VCDS. Just bought my first Skoda (come a long way since the 90s lol).

Problem I have is one Iv seen before on other ppls cars but never had to confront it so far. The blue temperture warning light comes on intermitently. This seems to be a common fault. It looks like someone had tested the winring back to the ECU before judging by the new leccy tape. All I have done so far is replace the 2 wire temp sensor. It has a good earth (continuety and battery voltage) and showing 5v unpugged and varies with temp. My first thought was maybe a quality issue with the instrument cluster (like the vw fox alert speaker) but I dont see this as engine sensors go straight back to the ECU. 

So assuming the wiring is ok I thought I save some time and ask on here wether anyone has traced this problem to a faulty ECU ? Iv googled around and just found the usual dumb stuff like 'have you checked the tire pressues' etc, etc. Anyone encountered this issue before ?

Thanks. Paul.

*although this could still be a fault between the ecu and the cluster or just on the cluster alone.

** Bear in mind the fault is logged within the engine module and no where else.

As you have figured out, the temperature sensor is driven/read by the engine ECU, and the results communicated to the cluster only via CAN messages.

 

If I were trying to pin this down I think I would log (with VCDS) coolant temp as reported by engine ECU during some driving, and look for any glitches in the data; or generally implausible numbers.

 

20 minutes ago, mamba76 said:

assuming the wiring is ok

I wouldn't, in fact I think that might be my prime suspect. Do you have pinout info? Any moisture in the connector at engine end?

 

Engine ECU fault really unlikely I think.

Edited 30 March, 20233 yr by Breezy_Pete
sp

Hi thanks for your reply.  Unfortunately I have no technical docs at all for this so winging it at the mo. If glitch in data is found still don't know if cause is ecu or wiring unless - I cut the two wires close to the ecu and maybe connect a suitable resistor to show the ecu a constant 1 volt or something (about 90 degrees i guess) and eleminate the wiring all together ?

Iv done a lot of corsas and ecu faults were very common but because they are more crap and expensive now, Im doing VAG only due to ross tech.

Maybe I might try and use the max value on my DVM and check once it comes back if it went over 5 volts but still could be either.

I will test the wiring tommorrow, It could be a CAN fault between IPC and ECU and only register on the ECU, CAN can be weird like that.

then again No comms would be the result.

 

Edited 30 March, 20233 yr by mamba76

Furnish me with engine code or VIN and I can give you pin numbers at engine ECU  tomorrow.

TMBAA25J193122151

Your a top man Pete. Cheers

Anything vauxhall, let me know ...

When solved I WILL post on here 👍

White wire from pin 1 at sensor connector goes to ECU connector pin 74, brown earth goes via a splice called 'sender earth' in the engine loom to pin 54.

 

 

Is so nice to have details like these, really appreciate it.

if that brown goes elsewhere then my initial plan of cutting and running an exclusive pair from ecu to temp sensor will cause problems.

I always see it as the ecu supplys the earths to each of it sensors rather than the earths going to the ecu, Normally each sensor has an exclusive earth so thats interesting. Do you know what other sensor(s) are supplied from that splice?

Thanks.

 

 

Others that share that splice are G42/G71 IAT/MAP sensor and G40 Cam position sensor.

there you go... cam sensor or crank would be one of my guesses. I thought you were gonna say all of them lol. So there are other earths on that socket of the ecu. Chances are its one of these shared components that are less sensitive than the temp sensor. Should be able to pull of the cam sensor once running. Ill have a play with it later and report back! May have to use my 80s oscilloscope so that'll be nice. 👍

Well this is embarrasing. In my defense I have no documentation or owners handbooks and this car was advertised with a temp fault when I bought it last week.

According to Skoda a blue or green light simply implies that a utility service is active! ie its supposed to do this. 

The blue symbol I thought was to do with coolant temperature may be oil temperature still not sure.

When the car is luke warm / cold the light comes on and after a few minutes running it goes off.

Just fitted a new timing chain kit and service but the car always ran perfect. 

Also found that VCDS only provides 2 output tests for the engine so will test cooling fan the old way. So far then no real problems but will come back if I find any. Thanks for your help Pete.

 

* although there was a P16502 so Im gonna stop here till Im sure if / what any problems I actually have.

Have you still got the sensor that you pulled out?

Had same error on our Fabia very recently, seemed to give OK temp numbers but kept logging that fault, even put the EML on while missus was out and about.

Replacement fixed it, and only thing apparent when examining old one was that the junction of brass to grey plastic had gone a bit loose; could twist the two bits relative to each other through a small angle with little effort.

Rad fan testing by linking radiator thermoswitch connector:

Edited 31 March, 20233 yr by Breezy_Pete

yeah will check the one I took out, only cheap so put a new one in.

The rad with fan are brand new after market type Im sure its ok at this end tho am yet to get the fan on by itself. Went to 99 degrees and nothing so switched off. I need to take it out on the road and boot it to be sure its bled properly but got bumper off ATM. Im getting new MOT mid week so we'll see if there are actually any problems, for now all seems well!

So do you get the blue light on dash until engines warms up a bit?