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Old 25-03-2018, 08:39   #1
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No GPS signal... in truck?

Hey all,

Hopefully the mods will let this one slide as it's related to boat nav software... although when I have the issue it's not on the boat.

I recently picked up an old Toyota 4wd pickup as a beater/work truck to make runs to the boat yard, dump, etc. My sails, boat cover, etc don't fit in my regular ride.

Anyhow, I noticed the other day that with the truck running, sitting in the cab with the door shut, I couldn't get a GPS fix on Navionics, Google Maps, or Waze on my phone. I reset the phone a few times with no luck. I've noticed this happens pretty consistently now and in multiple locations - not just my boat yard.

The odd thing is that if I start any GPS software outside the running truck, get a fix, then enter the truck and shut the door, GPS will work just fine for the drive home. (I use GPS software to avoid traffic.)

The truck is old, but in fine driving condition - the one odd thing is there is an issue where the radio won't turn off and constantly makes a very low hum - barely audible when driving.

Is it possible it's creating some sort of GPS interference inside the cab?
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Old 25-03-2018, 08:55   #2
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Re: No GPS signal... in truck?

Does the GPS work before you start the motor?

Is this a gas/petrol engine? If so, the spark plug wires and/or distributor may need to be renewed. As they age and crack they can leak during the spark event and radiate all kinds of RF interference. I doubt the car radio is the problem.
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Old 25-03-2018, 09:03   #3
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Re: No GPS signal... in truck?

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Does the GPS work before you start the motor?



Is this a gas/petrol engine? If so, the spark plug wires and/or distributor may need to be renewed. As they age and crack they can leak during the spark event and radiate all kinds of RF interference. I doubt the car radio is the problem.
^^This - and along the same lines, I would also take a look at the supressor.
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Old 25-03-2018, 09:06   #4
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Re: No GPS signal... in truck?

Interesting. Always knowledgeable folks here. Thanks transmitterdan.

I haven't tried starting GPS inside the truck without the engine on. I will now. Yes, it's a gas/petrol engine. It's a 1996, so fuel injected. Distributor and spark plug wires are easy enough to replace if that's the issue.
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Old 25-03-2018, 16:14   #5
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Re: No GPS signal... in truck?

old hand held gps's never worked well inside cars. because of the metal. it had to be under the windsheild with a veiw. newer ones like phones are much better now though. and should work.
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Old 25-03-2018, 16:56   #6
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Re: No GPS signal... in truck?

Download "GPS Test" from the Play store, it is a classic app that will show you exactly how many satellites your phone is receiving, whether it has a lock, what the signal strengths are. See what it says, they check again after the truck is running. I would expect that if the truck is creating interference you should be able to see a change in the signal levels.

Any fairly recent call phone should be a G3 or G4 chip and work very well in a car or truck cab, but free apps can show you exactly what they are seeing.

There are some windshields that have a metallic film in them (Lincoln was notorious for this, using a gold film for "fanless" defrosting) and that can block cell and GPS signals. Your traffic information will be coming from cellular data connections (more free apps to monitor them) and not from the GPS. There are also side window tints, some factory others applied as films, that are also mirrored or metalized and block signals. But even if the windshield is metalized, you should get enough signal through the sides for them to work.

Free apps. Objective numbers.
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Old 26-03-2018, 08:44   #7
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Re: No GPS signal... in truck?

It would appear to me that it is shielding by the cab. If it were an electrical interference issue only I would think the problem would exist out side the cab but in close proximity to the engine, radio or whatever. Or a combo of both.
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Old 26-03-2018, 08:48   #8
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pirate Re: No GPS signal... in truck?

I have this issue in steel boats.. thats when my 3 metre USB cable on the magnatised puck earns its keep..
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Old 26-03-2018, 11:39   #9
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Re: No GPS signal... in truck?

Older GPS units struggled when inside vehicles and buildings unless next to a window - modern ones do much better but still can't receive through shielding (metal cab). Some of the latest GPS modules have dead reckoning abilities - magnetic heading and accelerometer - which allows a continuation of position reporting when the GPS signal is lost (think tunnels and canyons - natural or urban). Clearly this doesn't work when the GPS is first turned on, but after acquisition it should. I doubt this is what is happening, but it is possible if it is a newer GPS.

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Old 26-03-2018, 12:48   #10
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Re: No GPS signal... in truck?

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I have this issue in steel boats.. thats when my 3 metre USB cable on the magnatised puck earns its keep..
Yep, I use one in the jeep where cab + forest leads to a week signal. They are cheaper than new plug leads!
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Old 26-03-2018, 18:34   #11
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Re: No GPS signal... in truck?

Most likely difficulty in GPS acquisition when begun inside truck. Ignition noise the probable cause. Initially acquiring satellites is more difficult than continuing tracking once acquired.
Try a marine handheld radio inside the cab with motor off then running. Any change in background noise or squelch level?
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