With the following steps you can reset you iPhone memory. This has a possitive effect on the incoming GPS information. With this reset all of your internal memory will be deleted. So it's absolutely necessary to back up your iPhone (see point 1)
- Follow the instructions of the Apple support site to back up:
- Put your iPhone on the charger.
- Go to Settings > General > Reset.
- Tap then on Erase All Content and Settings and accept the deleting process.
- The deleting process can last up to two hours depending on the size of the memory.
- After the deleting process connect your iPhone with iTunes or the iCloud.
- Now play your backup to your iPhone.