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No 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.

Where is Click and Clack when I need them, td

It could be most anything, but whenever I have an rf problem that is affected by my body’s relationship with the receiver first thing I suspect is the receiver and antenna are not grounded properly. If the GPS unit and its antenna are part of the same module, about the only thing you can do is make sure it has a good ground connection. If the antenna is separate, make sure the ground on the unit has a good connection to the antenna ground and shield and both are connected to the chassis body at some point, usually near the antenna base. If you don’t find anything from a visual inspection, you’re probably looking at a replacement GPS unit. You might get lucky and find that an insect has built a web in or on the GPS unit I suppose. I’ve had that happen with microwave receivers.

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Old fashioned paper maps? I means WTH vinyl records are making a come back, why shouldn’t traditional paper maps. But they are a pain to fold.

George, I think the OP has hand held GPS units, so grounding to the car ground is not possible.

Since it only occurs with one car, then that car is emitting RFI (Radio frequency interference) on the right frequency to ruin the signal from the GPS satellites. It would take an expert with the right tools to trace that RFI, but perhaps some general fixes may work.

If it doesn’t depend on engine speed, then you can rule out ignition issues. If it has an electric fuel pump,that is a good candidate. The alternator is another possibility.

To check the fuel pump, turn the ignition on without starting the car, and see if you get the interference…

It might be the heated wiper rest embedded in the windshield. This was a place on the windshield that heated the wipers so the blades won’t freeze on 02 to early 04 T-birds. It might interfere with the GPS signal.

This may be similar to the electrically heated windshields used in some cars in the late 90’s and early 2000’s. They gold foil layer in the glass to heat it completely blocked the signals to radar detectors. It would block GPS and phone signals, too.


Mustangman, OP said he has the problem with the GPS unit outside the car but within 20 feet. That rules out foil in the windshield blocking the signal.

I spent 10+ years installing CB, car stereo, two way radios. Fords (especially upper end models) would almost always present problems with the radios. This is a problem you may not be able to rectify (cheaply).

Ok, missed that.

Have you tried swapping the bad GPS unit with one from one of the other cars?

Also, what kind of GPS unit are we talking about here? You didn’t tell us anything about it.

If your iPhone GPS works fine in the Thunderbird with the engine on, then I’d start suspecting the unit or the unit’s power cord, or electrical interference coming up the power cord from the vehicle. Disconnect it and run the unit on battery (if applicable) to see if the problem goes away.

@GeorgeSanJose George, I felt that at least I knew these were portable GPS units, apparently you did not really know what was being discussed. Why you feel you have to try and answer a post without a clear idea is puzzling.

Out of curiosity, does your AM radio reception on this car have much more noise than on your other cars? Electrical interference can often be heard on the AM radio band.

Shadowfax, these are handheld portable GPS, and he tried three of them.

These units could be the type that set on the dash or suction cupped to the windshield or the type used by hikers and hunters to find their way back. But it seems a call to the manufacture of the units is in order here.

Thanks, I will look for some of the things you were referring to however my GPS is a portable GPS and it works perfectly fine in the other vehicles. Could the car antenna, not grounded properly, interfere with a portable GPS?

So what is different, do you have an mp3 fm transmitter in the car? What other devices that may use the same frequency

If your radio works in both AM and FM properly that eliminates the vehicle antenna.

Have you looked at the GPS makers web site for help?

no (10 letters)

One time I had an rf interference problem where I lived, AM radio interference. I traced that to the rooftop tv antenna grounding and shielding. It also involved the tv set. I ended up running the tv set on an isolation transformer, rather than directly plugged into the wall, which by trial and error turned out to be the easiest way to reduce most of the AM radio interference. Whether that would apply to your GPS, seems unlikely. The way I figured this out was by disconnecting the antenna at the tv, which reduced the interference. So you could try that if you wanted to get all scientific-like, disconnect the antenna radio at the radio, see if that helps.

There’s a relationship between the size of the rf openings (like the windows) in the car and the wavelength and how much gets through. If the wavelength is near to the size of the window opening for example, how much rf energy gets through will be pretty sensitive to that. A slightly bigger window opening could allow quite a bit more rf in. Don’t know what the wavelength is for GPS tho. I think it is quite a bit smaller than the size of a car window. If so, that wouldn’t apply in your case. The only other thing I can think of is if you have anything different about the window glass in that particular car. Is it tinted or anything like that, different from the other cars. If there is any metal in the tinting, that could make a difference I suppose.

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