Bluetooth in call volume problems

[BenKentzer]

Hello!

I've done a few stereo based upgrades on my R Line estate, and now have the following:

RCD510DAB
MDI in glove box (Passat CC drop down flap)
9w7 (I think) bluetooth module under the passenger seat

The RCD 510 appears to be coded fine for both the MDI and the Bluetooth - the iPod works perfectly (most of the time) and I can connect iPhone 4S, iPhone 6 (just upgraded) and HTC One (original) with no problems. Phone book downloads, and I can make and receive calls.

I've not currently got the microphone connected, but...

If I turn the volume right up on the RCD510 when in the middle of a call, I can just about hear the call - not quite enough to actually hear what is being said. Pretty much defeats the object of the unit, to be honest.
I tried a bluetooth volume app on the HTC, but it made no difference. If I can get it to work with the iPhone 6, then I'll be very happy.

I've never had the car coded for the bluetooth module or the MDI, but as both appeared on the RCD510, I figured it was probably okay. It therefore doesn't appear to display anything on the MFD for the phone, but it puts the track names on from the iPod.

It's going into the dealers for MoT (plus cam belt & water pump - special offer just when I needed it!) next week, and I just wondered if there was anything I could try to get them to do (coding etc) that might actually help it work. I'll get the microphone connected up if I get a chance before hand, but any advice would be gratefully received...

Cheers

Ben