Mercedes Audio 20 Bluetooth Nightmare

[blueST]

We have a 58-reg A Class with the Audio 20 stereo. It has DAB and the Media Interface, just in case that makes a difference. I cannot get a mobile phone to reliably connect via Bluetooth. I'm not normally stupid when it comes to stuff like this, but I'm totally baffled now, and am wondering if something is faulty.

I have tried two separate phones. One is an Android smartphone, the other is a cheap Samsung touch screen job with Samsung's own OS. In both cases, I can authorise the phones with the Audio 20 fine, and the phones appear in the list of registered devices. At this point, all appears fine, I can make calls, transfer contacts etc.

The problem comes when a phone tries to connect again the next time I'm in the car. Again, in both cases the phones themselves think they are connected to the car, because they both show their respective Bluetooth connection logos on screen, but they don't show as connected on the car stereo and I can't make calls via the stereo.

The only slight difference is, with the Android phone, the stereo display briefly shows the "connected to..." message when I start the car, it might flash up a couple of times, but it eventually goes away and stereo reverts to thinking it is not connected to the phone. With the Samsung, nothing happens at all.

Things I've tried so far:
Only having one, or other of the phones registered with the stereo.
Making sure Bluetooth visibility is on.
Deleted all other Bluetooth connections from the phones.
Deleting all registered phones from the stereo and starting again.

Can anyone suggest anything, or decent methodical way of troubleshooting the problem?

[Sgt Bilko]

In the bluetooth connection settings (on your phone), have you got "automatically connect" or similar selected under the pairing for the car?

[blueST]

Checked that, both phones seem to be set correctly. Both of them show the Bluetooth headset symbol when they are in the car, which makes me think some sort of connection is happening.