Coolant Light flashing on start up.

[silver4444uk]

Hello Everybody,

This is my first visit to the Polo forum.

I have just bought a 2002 1.0 ltr Polo for my daughter as a car to learn to drive in.
The seller did warn me that the red coolant light was continually flashing, immediately after start up with the engine cold and at other times intermittently. The coolant temperature does warm up after a few minutes to approx 90 degrees on the guage and it does not overheat.
I have looked at the coolant level and it is correctly filled in the expansion chamber.
When the car warms up the thermostat does operate because the top hose to the radiator does warm up.
There appears to be no problems with the head gasket because there are no bubbles coming into the expansion tank when reving the engine.
Also I have put Vagcom on the car and there are no faults listed.

I suspect it is the level sensor in the expansion chamber. I put a multimeter across the terminals and it is indicating open circuit with the expansion chamber correctly filled. I can't find any details anywhere to tell me what the resistance should be.

Can anybody tell me, firstly if my fault diagnosis is right and what resistance I should be looking at ?

I guess that I will have to change the expansion chamber as it looks as if the sensor is built into it.

Any pointers would be greatly appreciated.

Thanks,

S.

[Doctle Odd]

It's the header tank, cheap and easy fix the sensor goes in them regularly

[silver4444uk]

Thanks for the rapid reply Doctle Odd.
I will change it this weekend.

Rgds.

S.

[silver4444uk]

Well I replaced the expansion tank today and the coolant level light is still flashing after the ignition is on or engine has been running for a few minutes.:(

So I'm guessing (assuming that I got a good expansion tank ), that I'm looking at either a fault within the instrument cluster or a wiring fault.

Can anybody tell me please:
1) Is the circuitry within the dash replaceable ( e.g. a printed ciruit board) or do you have to buy a complete instrument cluster from an internet auction site, scrappy or similar ?
2) Regarding the sensor within the expansion chamber is it a simple switch (as shown in the Haynes wiring manual ) or is it a capacitive sensor ? The reason that I think it
may be capacitive is that again when I've put a multimeter across the terminals with the tank correctly filled it gives a very high resistance, typically 2MegOhms (the resistance on my old tank was approximately 6MegOhms).

My plan is to take the instrument cluster out and check the wiring from the connector on the instrument cluster to the connector on the expansion tank.

Any tips/ suggestions / info. would be appreciated,

Rgds.

S.

[silver4444uk]

I took a hacksaw to my old expansion tank today and guess what it is a capacitive probe type level sensor within the tank and not a switch as depicted in the Haynes wiring diagrams.
So that's one of my questions answered.

[Doctle Odd]

VWVortex.com - Coolant Level Sensor Delete (http://forums.vwvortex.com/showthread.php?4633010) dunno if you just want it out or to fix the problem, usually a new tank sorts it

[silver4444uk]

Thanks for the post Doctle Odd.

I want to fix the problem as I want a "coolant low level circuit" that is going to work and tell me when I have a problem.

I removed the instrument cluster this evening and checked the wiring from the connector at the rear of the instrument cluster to the connector at the expansion chamber, and it was good.

So assuming my replacement expansion chamber is good, I am now on the prowl for a replacement cluster.

I have to admit that I don't know where on the car the actual mileage is "stored".

Can anybody tell , if I replace the instrument cluster will I still keep my original mileage or will it change to that of the replacement cluster ???
If it does change to that of the new cluster what are my options ?

The car has only covered 49k miles and I would like to keep it genuine.

Rgds.

S.

[Doctle Odd]

The mileage is stored in the cluster. A different cluster has to be coded in with VCDS or you can bring it to a dealer. You will also need the PIN code for the car. A used cluster can have the mileage "corrected" with software available from well known auction sites but a used cluster is a false economy IMO. I believe VCDS will allow one time only mileage adjustment on a new cluster. I estimate min £250.00 for parts labour and coding.

[silver4444uk]

Doctle Odd,

Thanks for all of your replies and tips, they have been very useful.

I cannot justify spending £250 on a new cluster, when the car did not cost much more than this.
I am going to keep the original cluster and put a shorting link on the connector going to the expansion chamber (as was suggested in one of your posts ).
I tried it last night and with the shorting link in place the light stops flashing after switching the ignition on.

My daughter will have to keep an eye on the temperature guage and check the coolant level regularly. Or should I say her dad will be checking the coolant level regularly !

Thanks again,

Rgds.

S.

[Doctle Odd]

It will be part of your weekly checks mate. Generally they don't use coolant and if a leak develops the thermometer icon will light up (I think) and obviously the temperature hand will rise. :beerchug:

[silver4444uk]

Aaaaargh, it's back !!!

Well I thought that I had got rid of the pesky flashing red coolant light by putting a shorting link in the connector , but the fault came back after a few days.
I have read in the VW literature for my car that the flashing red coolant light lights up not only for low coolant level but also for excessive coolant temperature.

Can anybody tell , me please where the cluster gets the excessive coolant temperature signal from ?

Does the coolant temperature sensor (green one ) send it to the ecu and then to the dash ?

The Haynes manuals are not great when it comes to wiring.

[Doctle Odd]

The problem might be with the cluster, did you ever get a VCDS scan?

[silver4444uk]

Yes I have scanned it with Vagcom and it is showing no faults.

But I don't know how good Vagcom is at showing up this sort of fault.

Doctle Odd do you know where the cluster gets the coolant temperature signal from that puts on the flashing red coolant light ?

[Doctle Odd]

I always thought it came from the sensor, electrics aren't my strong point. Vag.com will allow you to scan the instrument cluster, if you're using 409 upgrade to VCDS lite its free to do so

[silver4444uk]

Thanks for the quick reply Doctle Odd,

I think that if the wiring on the Polo is basically the same as on other VWs of the same age (MK3/4 Golfs), then the sensor will have 2 temperature sensing elements within it,
one sends a signal to the coolant temperature guage on the dash and the other sends a signal to the ecu primarily for controlling the amount of fuel / air mixture in the engine depending on temperature.


Please note if I am spouting rubbish with my theory above I am more than happy to be enlightened.

Which was why I was wondering where does the signal come from that can put on the red flashing coolant light,

other than the coolant level sensor in the expansion tank ?

I will have another play with the car this weekend.

Thanks again for your advice.

S.

[Doctle Odd]

I thought you had a low coolant level light flashing? That's an overheating light, if the car isn't overheating it's the sensor

[silver4444uk]

Sorry, I didn't intend to mislead you.

According to the VW Polo handbook that came with the car, the red flashing coolant light will light up for
either low coolant level or excessive coolant temperature.

The car is not overheating so I will throw a coolant temp sensor at it this weekend and post the result on the forum.

Thanks again,

S.

[Doctle Odd]

Mate it's my fault. I've never owned a polo so when you said coolant level sensor I assumed it was a separate light same as a passat a4 etc. I apologise for sending you the wrong way.

[silver4444uk]

No apologies needed Doctle Odd,
you have been very helpful with your replies,
I am going to try that pesky sensor this weekend and see what happens.

[silver4444uk]

I changed the coolant temp sensor this morning and the fault is still there so I'm guessing I have a faulty instrument cluster as everything else has been tried.

[Doctle Odd]

Bugger, did you try to remove the workaround you did and connect the level sensor again?

[silver4444uk]

Yes I reconnected the tank sensor, removed the shorting link and the fault is there.

I have ordered up a replacement cluster, as by my reckoning, I have already spent a couple of hundred quid doing the car up (timing belt, water pump, brakes, discs, shoes, servicing etc ).
So it will be worth it knowing that my daughter will see a " working" warning light if she starts losing coolant / or it overheats
and hopefully her younger sister will get a chance to learn in it as well.

Many thanks for your suggestions / fault finding Doctle Odd.

Rgds.

S.