[Roadster]

My nearly 1 year old Rio TGDi 2 has had this very infuriating intermittent fault. When its icy, below 2 C press the rear screen heater button and absolutely nothing happens. 10 minutes down the road and its all fine.Its been looked at once but obviously driving to the garage warms everything up and there is nothing to see.
What should I suggest they do? As far as I can tell there is not even a click from (is it a relay?) the dashboard when this happens.

 

[iooi]

Hi & welcome.

Have you looked in the main fuse box (engine bay) and checked if maybe the relay is loose, or some water in it?
Have you tried a multimeter on the wiring to see if it does have power?

TBH, never heard any clicks when switching any of ours on.

 

[Radiorail]

Is there a possibility that your battery is in poor condition and the control circuits for the rear screen heater won't engage until the alternator has 'topped up' the battery while the car is driving?

I've never come across this but can imagine that some designer could come up with it to make sure that the car was running on alternator before allowing other heavy electrical loads. Could also be an under performing alternator but that does not fit your 10 mins down the road observation.

 

[maxaret]

Our cars are quite slow to heat up and clear the rear screen.

 

[mr.macspot]

Our cars are quite slow to heat up and clear the rear screen.

Same here. It's okay for defrosting, a few minutes loosens the ice enough to scrape of with squeegee, but when it's demisting it can take a while.

 

[Turnup]

My nearly 1 year old Rio TGDi 2 has had this very infuriating intermittent fault. When its icy, below 2 C press the rear screen heater button and absolutely nothing happens. 10 minutes down the road and its all fine.Its been looked at once but obviously driving to the garage warms everything up and there is nothing to see.
What should I suggest they do? As far as I can tell there is not even a click from (is it a relay?) the dashboard when this happens.

You realise that the rear screen de-icer will take come time to warm up? If you watch it you should see stripes of clearer glass appearing quite soon (a couple of minutes) after turning it on.

 

[Roadster]

When I say nothing happens, I mean absolutely nothing. No light on the switch, no warmth on the element, its not switching on. Then after the car has warmed up... it works. It also works if its above 5 or 6 degrees.

 

[iooi]

When I say nothing happens, I mean absolutely nothing. No light on the switch, no warmth on the element, its not switching on. Then after the car has warmed up... it works. It also works if its above 5 or 6 degrees.

Radiorail may have hit the jackpot.

Check the battery.

If battery is on the weak side it is possible. Cold is a killer of batteries. Running car or higher outside temps will/might be enough to make the battery feel better.
Or it could be switch contacts, that when are warm are making contact, but not when cold.

Does car struggle to start?

 

[Radiorail]

I have just been out to the shops and conducted a quick test. On My Stonic the heated rear screen will not switch on (no light) if the car is in 'accessory' mode i.e. ignition on, all warning light alight, but engine not running. Other high current things do (seats & steering wheel) .

To me this indicates that the rear screen will not switch on unless the alternator is running and can provide appropriate current. I guess there is a voltage/current sensor that basically says "if battery is drawing high charge current supply that in preference to heated rear screen" - so that the battery can quickly recover the starting current it has lost and start the car next time.

 

[Roadster]

I had the same thought about battery condition,but it is nearly new, so have tried starting the engine, waiting for the engine note to settle then pressing the button. Same result, nothing happens. Of course I have to wait for cold weather to test it and its very mild today.Back to KIA I think but they must swap something out like the switch or something?

 

[Radiorail]

I had the same thought about battery condition,but it is nearly new, so have tried starting the engine, waiting for the engine note to settle then pressing the button. Same result, nothing happens. Of course I have to wait for cold weather to test it and its very mild today.Back to KIA I think but they must swap something out like the switch or something?

You really need to sit with high revs for a minute or two for the alternator/battery charge system to settle. It may be a poor connection at the battery.

 

[Roadster]

You really need to sit with high revs for a minute or two for the alternator/battery charge system to settle. It may be a poor connection at the battery.

This morning it was 4 C I pressed the button, nothing. As suggested I ran the engine for a couple of minutes, pressed the button and Bingo! pressed the button and on it came. Waiting for a cold night now to prove the theory.