What can interfere with GPS signal?
I have three GPS units and they all work fine in all of my cars except in my 2003 Thunderbird. As soon as the ignition switch is turned on, with the engine running or not, the GPS will loose it's signal. If I move away from the car about 20 feet the signal will return but as I approach the car the signal goes away. Works great in the car as long as I don't turn on the ignition switch. I have exhausted all of my options, with no positive results. Has anyone ever had or heard of this problem? td, no
ps... IPhone GPS works good, not a problem.
I really appreciate the input I am receiving; However, I will try and clarify some of the logistics so you may better understand the situation giving you an opportunity to give more relevant suggestions or solution to this puzzling problem.
: I have three Garmin dash mount GPS units and they all work fine in other cars.
:In this example the T bird is not running only the ignition switch is on. Does the same thing if the car is running.
:You do not have to be in the car with the unit (with the switch on) for the GPS not to function. I have disconnected the radio, heater fan blower, and Pandora. The Fuel pump will go off after a few seconds with just the switch on and the engine not running.
: I have been in contact with Garmin, talked to a few of their Tecs and they have never experienced anything like this.
: Bought the car in Houston three years ago, GPS worked good from Houston to Mississippi. Also from Mississippi to Dearborn. Started having trouble with the GPS there, bought a new one

Welcome to the site. Sorry, I don't know what could cause such a problem. But the next time my GPS loses signal, I'm going to check to see if there's a 2003 Thunderbird anywhere nearby.

But seriously, the part about the iPhone is baffling. Are you sure it has a "real" GPS fix and not A-GPS where it uses cell signals and wifi to approximate your position? One difference between newer iPhones and Garmin automotive units is that Apple has added GLONASS capability, which makes more satellites available. So maybe the RFI from your car doesn't interfere with GLONASS reception?

One practical solution would be to forget the Garmin units and just get the Garmin StreetPilot app for your iPhone. It looks just like a Nuvi.

Heh, you are probably violating some FCC regulations if your car really interferes with GPS reception.
That was my thinking too. The iPhone could be just using cellular tower location. The frequency of GPS is ~1575 MHz and is much weaker than cellular signals considering where it comes from!

Maybe you could see if you could exchange the car's main computer module with a different one. It sounds like heavy electrical/ rf noise maybe due to shielding or a faulty component. An expensive proposition but maybe a wrecking yard might have an exchange unit you could try. Although I have heard some of the newer ones have to reprogrammed by an expert that may not apply to one that old.

Some commonly used metal material may interfere with the signal. Also the possibility of someone is using a GPS jammer may also interfere or totally make the GPS signals near it unavailable. Nowadays, it's not rare that some guys use a jammer (cheap & easily got online) to stop others from tracking themselves or protect their privacy.
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