A global navigation satellite system (GNSS) receiver using phase lock loops for strong GNSS signals and automatic frequency control (AFC) loops for weak GNSS signals on a satellite-by-satellite basis. The phase lock loops or the AFC loops associated with particular GNSS satellites generate frequency feedback adjustments for tracking the carrier frequencies of the incoming GNSS signals in order to determine pseudoranges for calculating a location fix. The transition from an AFC loop to a phase lock loop is controlled for each GNSS signal depending on location quality parameters including a history of previous loop transitions, knowledge of whether a transition is in-progress, and a conditional PDOP. The conditional PDOP is the calculated PDOP where the pseudorange from the particular GNSS signal is removed from the computation of the location fix.