[AlanD]

Hi RXJ,

I see no one has responded to your post, so I'll offer a comment or two.

1. You dealer might be more on the ball than you believe. GPS satellites have a period of 2 orbits per day - they are not synchronous - and so they move relative to a fixed point on the ground. When they drop to low angles the signal strength, which is quite small to begin with, will fall. Ordinarily this isn't a problem since usually there will be reception from enough sources to maintain a good positional fix - but you might get an occasional drop out if the GPS receiver can't "See" the minimum number required.

2. Paradoxically CBD areas are quite "poor" reception regions because of the tall buildings (usually full of reinforced concrete) preventing good reception from satellites that could be close to overhead but are shielded by buildings' structure. In this event the receiver can drop into "dead reckoning" mode (like going through a tunnel) until enough satellites have come into view. Dead reckoning can be confused in CBD areas because there is no guarantee you are going to keep going straight ahead. With a tunnel there is an entrance and a exit and the software is usually good enough, with input from the car's speed data to get you to the exit at a time when satellites get reacquired. So no apparent drop out occurs.

You do not say if the fault is a) complete shutdown (I have had this happen once and was blind until the system rebooted) or b) telling you that you are located where you know you are not ( also had this happen once in Wyoming where the GPS was saying we were about 400m north of the highway we were travelling along and wanted me to turn right to reacquire the highway).

Either way, I regard the in car system as being less accurate than my trusty TomTom unit ( which has the advantage of a speed readout that is rather more accurate than the car's speedometer)

Let us know how you get on

Cheers