iPhone mono sound only on car stereo My iPhone 3GS (iOS 6) has started playing out of the left speaker only on my car stereo.  Before the new software release, it was playing out of both speakers.  When I switch to radio mode on my car hi fi, it will play from both speakers so it appears to be an iPhone problem rather than a problem with my car hi fi.
iOS 6 has a new setting to mix the sound. I would check there first, and then see about other sources to see if it's particular to how you are routing the sound to the car (cable or bluetooth).

Hopefully, it's a software setting that got set on you as that's the easiest thing to correct.