Several users have reported an issue in which iOS devices (including the iPhone, iPod touch and iPad) are rendered incompatible or exhibit issues with various USB-based car stereo integration kits after the update to iOS 4.0.
Users have reported this issue with the following head unit and car brands:
There are several potential fixes for this issue, including:
Hard reset. Some users have been able to restore connectivity and eliminate issues by resetting their devices. Hold down the sleep/wake and home buttons simultaneously for roughly 15-20 seconds, until the screen powers off then an Apple logo appears, which signifies a reboot. Some problems may require (oddly) that this procedure is performed twice. Failing this, try the rest of the 4 Rs, listed in our iPhone troubleshooting guide.
Reset head unit or system. If you are connecting your iOS device you a head unit, try removing the face plate and pressing the small reset button with a paper clip. Alpine, for instance, offers these instructions:
“To reset the Alpine head unit there is a small indented button usually located on or behind the face of the head unit. This can typically be pressed with a pen or paper clip. Press and hold this button until the head unit powers down.”
Try such a reset in conjunction with the aforementioned iOS device reset.
Connect iOS device while it is off. Some users have reported success with connecting their iOS devices while off, then starting their cars, then powering on the iOS device.