DAB radio doesn't work in cold weather

[rsharpe]

Here's a strange one.

On a very cold morning the DAB does not work i.e. the radio says 'no reception'. The FM is very poor and unusable at the same time. After about 15 minutes they will both start working. Last winter I only noticed this below about 5C but I've already seen it this year at 11C.

I noted yesterday when activating the front and rear heated screens there was a harsh crackling from the radio on DAB. So I have no doubt there is at least one problem there. Thinking back over the last few weeks, on cold mornings I can see stripes down the front screen. I know that last winter when activating the heated screen it clears in stripes - I suspect some of the elements are not working. The stripes I've seen over the last few weeks happened when I did not have the heated screen on but there was condensation on the inside of the screen.

So now I'm wondering if the heated screen power electronics are 'leaking' so the screen is always on to some degree. And I'm wondering if this is all down to the same fault. At least now that I can tie down the poor radio behaviour to the heated screen I can ask the dealership to take a look. I don't think "it doesn't work in cold weather" is much to go on, and if I book it in we will have a heat wave and it will play nice. But the heated screen can be activated at any time so I think that is traceable.

Interested in any thoughts!

[mike020150]

On the face of it, it sounds to be an odd fault. However, since the heated window elements are used as radio antennae, the connection is less surprising. The antennae require a power amplifier to work so the issue may be linked to a fault with the amplifier and not necessarily the heated window elements. Jaguar diagnostics or the Autologic equivalent will probably be required to pinpoint the issue at stake. Mike.

[rsharpe]

Great, thanks Mike. Next time it goes in I'll ask them to look at it.

[rsharpe]

I checked this yesterday morning. It was 6C and the radio didn't work for the first 20 minutes of travel. When it eventually came to life, I confirmed that activating the heated rear screen kills the radio (I was on DAB). Turn off the heated rear screen and the radio comes back to life.

On a similar note, is there anything in the shark-fin on the rear of the roof, or is it just for show?

[mike020150]

F-Paces have antennae in the roof pod (shark's fin), the rear window and the spoiler, dependent upon the specification of the in-car entertainment and navigation systems fitted. Mike.

[Marineng]

There is also an electronic curcuit board located in the base of the assembly. Thermal contraction/expansion could have created a joint that goes open circuit at low temperatures or electrical interference screening could be breaking down. Is there an option to shut off the heated rear window as soon as you start? in addition if you turn on the heated rear window when the temperature rises does this affect the radio?

[rsharpe]

Thanks Mike and Marineng for the inputs.
I'm wondering if there are two different issues. The early morning 'no reception' issue is not only dependent on temperature I think its more about humidity. I say this because on a cold afternoon the radio works fine, so the only difference is that it appears to fail after overnight temperature drops, and there is inevitably condensation. But it's OK in the rain! I'm thinking that on a cold afternoon the car has had 8 hours in daylight, maybe even some sunlight, so despite the low temperature, it works OK. I do believe 'cold and wet' air overnight is the problem. Rain is probably not getting in the aerial module, but the air in there is cooling and creating condensation? It does sound exactly like a cracked circuit board or joint. My problem would be how do I get the dealership to change something (the shark fin aerial?) when there are only certain atmospheric conditions that cause the problem. The car would need to go in during November to March, stay overnight in the car park, and not be taken inside to fix! How easy is it to remove the aerial and take a look inside? I had a similar problem on an Audi estate and the aerial was full of cobwebs. I re-soldered a couple of dry joints and it came back to life.

The discovery of a link to the rear window heater is quite new, and I don't think it's temperature related. On a very cold morning the radio would not work anyway, so using the heater is transparent (I wouldn't know whether the heater is affecting the radio). But I did try the heater on a warmer afternoon (when the radio was working OK) and it definitely kills the DAB. So that's why I'm thinking it's a separate issue.

It's all interesting stuff!

[JimMann]

I suspect your problem is fully related to the interconnection between the heated rear screen and the fact that it doubles as the antenna for the radio. On colder days / nights, the heated rear screen should come on automatically, without you activating or touching any switches. Accordingly, your initial impression that the radio wasn't working on cold mornings would likely have been related to the automatic switch on of the heated rear screen. Same will happen during any other time of day if the car "thinks" the rear screen could be misted for any reason, the auto switch on would occur. Not sure if it has an actual temperature limit, but if you check the indicator switches (for the heated screens) you should find that they come on without your involvement.
Similarly for the "partial" clearing of the rear screen when you have not activated the switch, it has likely been switched on by the car and then immediately off once again. They get too clever by half sometimes.
Jim

[rsharpe]

The diagnosis was that I needed a new rear screen, as the DAB aerial is combined with the heater (as already pointed out). It took a while to get the warranty approval and to organise screen delivery, plus the specialist to fit it, but that is now done. The weather has got much better since then so I can't be sure that it has been fixed - we'll have to wait for November to get the next exciting episode!

[mike020150]

Glad it's fixed under warranty. That could have been an expensive repair without a warranty. Mike.

[Marineng]

An excellent result
Paul

[rsharpe]

For anyone who is curious, today at 6AM the temperature was 13C and the windows were covered in condensation, after the hottest day of the year. As I drove away I noticed the rear screen demisting itself. There was no indication on the dash, so no indication that the rear screen heater is ON but the stripes undoubtedly appeared as the screen cleared. Either the power for the DAB aerial is enough to generate heat to clear the screen, OR the heater is constantly ON despite getting no signal from the pushbutton on the dash.

There is a remote possibility that the car knows the rear screen is fogged so it de-mists it, without activating the light on the dash, but I think that's a bit of a stretch. When the temperature is lower than ~4C it automatically comes on, and so does the indicator.

Very odd. What we really need is a manual that describes how the car really works. I guess that's only available to Dealers?

I won't be taking it in for any diagnostic. I already have a chair with my name on having been there so many times - this one I'll just live with. At least the radio works now!

[mike020150]

You'll have to put it down as one of those things that gives your car 'character'! Mike.

[chris839]

The DAB antennas are in the left quarter window and one of the foils ( the right one if my memory is correct )within the spoiler. I know that does not answer your question, but you can dismiss the rear screen.