Same problem here with iPhone SE, recently upgraded to iOS 12 and Citroen C4 (2013). The bluetooth connection to the previous iOS versions was also so-so, but usually was working. This time, exactly like the topic owner - have I tried all of the above without success. The problem is definitely with iOS. Which iPhone do you guys have?
The newer button starter C4 Picasso diesels do indeed take longer to start when the temperature drops below 3 degrees centigrade. The key operated ones seem to behave differently. I used to press and hold the button until I was told that you should press it briefly and release.
I think I resolved it by deleting the pairing, switching the phone off and on again, and then starting the process all over again. Also make sure the phone is 'discoverable' - sometimes it's in the Bluetooth settings. I'm not sure how exactly I got there, but I did in the end!
Today my wife took the car to The Citroen Clinic in Nottingham for an initial diagnosis (great service so far by the way). By listening to the noise on tickover, the guys strongly suspect DMF wear, requiring a DMF and clutch replacement.
Out of interest are you listening to DAB radio stations when this happens. Sounds stupid i know, but i usually listen to bbc6 music for a number of months and then recently this problem started. A colleague said it was due to radio data broadcast with signal. He said try another station and problem will not happen.
Citroen C4 Picasso is a versatile, stylish MPV that represents terrific used value Bluetooth, rear parking sensors and alloy wheels. Issues with the braking system led to another recall in qF3NA.
