Coolant temp/level light flashing but both ok?

[roadrunner]

the coolant light flashes erratically, sometimes after 30 secs with cold temp and others after 5 mins with cool or hot engine.

Changed header tank and kept same coolant - no change.
Drained and re-filled new G30 coolant - initially thought fault had gone but re-appeared after a 3 min drive
Coolant temp stays at 90 deg max on dash.
Coolant level is fine - no leaks.
Coolant is flowing into header tank - pump ok.

Have inspected and cleaned terminals to sensor on header tank suspecting intermittent electrical issue - still happening.???

Any ideas welcome PLEASE.... Thx

[RUM4MO]

That might leave you with one thing, a wiring/soldering issue, ie the lead going to that indicator in the cluster having a dry joint so needing re-soldered, or a connector going to the cluster ie at the cable form going into the dash cluster.

I'd think that if you had VCDS or very similar, you would be able to find out if this warning was true and being sent out to the dash cluster - as opposed to a wiring/soldering issue causing this indicator to "switch on".

[Johntheo1]

the coolant light flashes erratically, sometimes after 30 secs with cold temp and others after 5 mins with cool or hot engine.

Changed header tank and kept same coolant - no change.
Drained and re-filled new G30 coolant - initially thought fault had gone but re-appeared after a 3 min drive
Coolant temp stays at 90 deg max on dash.
Coolant level is fine - no leaks.
Coolant is flowing into header tank - pump ok.

Have inspected and cleaned terminals to sensor on header tank suspecting intermittent electrical issue - still happening.???

Any ideas welcome PLEASE.... Thx

Just remove the coolant level sensor plug and drive the car for a while with it removed and see if it makes any difference, it should either flash continuously or stay a solid red or whatever the LED colour is.

[RUM4MO]

Just remove the coolant level sensor plug and drive the car for a while with it removed and see if it makes any difference, it should either flash continuously or stay a solid red or whatever the LED colour is.

Actually, just unplugging the lead should make the indicator stay OFF, for some reason, I have recently checked "how" the coolant level sensor works, and it is only a simple float switch that is open circuit until the level has dropped well below minimum level, at which point it is a short circuit. (I bought a used brake master cylinder complete with its reservoir cheaply to use as a test rig for my annoying Gunsons Ezibleed kits!). The brake light hall sensor might also come in handy, as well as the empty master cylinder to test the brake switch wiring - maybe.

Edit:- though that last bit of that concerning the brake light switch is only relevant to much later versions of Polo etc.

[Johntheo1]

Shorting it out so should put it in alarm mode, at least testing it both ways might rule out anything to do with this bit of the wiring circuit. There's a 2005 9N Polo in the family so I will do a few tests when next I see it.

[Johntheo1]

Just remove the coolant level sensor plug and drive the car for a while with it removed and see if it makes any difference, it should either flash continuously or stay a solid red or whatever the LED colour is.

Actually, just unplugging the lead should make the indicator stay OFF, for some reason, I have recently checked "how" the coolant level sensor works, and it is only a simple float switch that is open circuit until the level has dropped well below minimum level, at which point it is a short circuit. (I bought a used brake master cylinder complete with its reservoir cheaply to use as a test rig for my annoying Gunsons Ezibleed kits!). The brake light hall sensor might also come in handy, as well as the empty master cylinder to test the brake switch wiring - maybe.

Edit:- though that last bit of that concerning the brake light switch is only relevant to much later versions of Polo etc.

Yes, correct, in the March 2005 Polo 9N, no alarm/light when I removed the plug with ignition on but the sensor certainly doesnt appear to be a simple float, the only reading I get is to put the M.meter to 20 k.ohms resistance, when I probe the pins it briefly indicates ~ 18 k.ohms and then goes "open circuit" so probably some form of capacitance?, the wiring harness tells me nothing , no voltage between the pins and none from either pin to earth, (ignition on).
The 2019 Polo readings are exactly the same except that the alarm logic is different, when you remove the plug with ignition on it displays "Check Coolant Level" or words to that effect.

I didn't have the courage to short out the sensor plug.