I have an iphone 4s running IOS 6.1.3. It only stays connected to my bury handsfree car bluetooth system for approx 40sec before disconnecting. My wife also has a 4s but running IOS 6.0.1 and there is no problem, why might this be?

I have an iphone 4s running IOS 6.1.3. It only stays connected to my bury CC9060 handsfree car bluetooth system for approx 40sec before disconnecting. My wife also has a 4s but running IOS 6.0.1 and there is no problem, why might this be?

I thought it might have been a difference in applications between the two handsets. I discounted this as a possible source by completing resetting my phone. The problem persisted, hence my assumption that it is an IOS version issue. I haven't had the car and kit for long so I don't know which particularly update causes the problem. All I know is that IOS6.0.1 works and IOS 6.1.3 has the problem described above.

I am trying to arrange to update the firmware on the bury - but this has proven to be difficult.