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Key fob remote entry working intermittently

Doubt Incarnate

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Ok this happed twice today. the truck wouldnt respond to the remote, i tried to lock, unlock, hit the panic and nothing happened. tried the other remote too and all that worked was panic, it set it off but didnt stop it. later i went out to go to work and hit the unlock button and it worked, everything was fine. i replaced the batteries ($4 each!) but after i got home it quit working again. is it possible they need to be reprogramed (reminded)? i read somewhere that you can only program up to 4 remotes to one car and after that the module needs replaced. or is it 4 at one time and i can just keep replacing them?
 



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cybergasm

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Don't think reprogramming the remotes would help since they like the module tha controls the whole shebang have permanent memories was thinking that maybe it could be failing to work due to a dirty contact in the remote or localized interference since it appears it happen at home from what you said in ur post. And yes u can program up to 4 remotes per vehicle. Can't offer much help on this since i never had this problem with my Explorer.
 






jp450

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When ever I go to a peticular store my remotes will not work. There is a microwave tower in the area that messes up the system. Try relocating and test it. Keep in mind that the fobs do not have very much transmitting power and other sources of RF (radio towers, microwave links etc...) may cause it not to work properly.
 






Doubt Incarnate

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it didnt work in the am, and it works fine when im at work. it just irks me that it was working normaly at home up untill yesterday. i could sit on the couch and lock it up over 30 feet away through a brick wall, but not anymore. with all the expansion going on everywhere with subdivisions and condos, i wouldnt besuprized if a tower popped up overnight somewhere near me. thanks for the help
 






jp450

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I bet ya that is what happend. There is probably a new microwave link, cell tower or other source of RF in the area that is interfearing with your fobs.
 






NW Explorer

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Ive had to stop using a Gas station every time i go there car wont start immobiliser sticks.
 






blackmore

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immobiliser problem

I live in the U.K. and am experiencing the same fault caused by RF signals from the Ministry of Defence and police radio overpowering the key fob !!
Has any found a solution to the problem ? Can the system be switched off, overidden or modified in anyway to prevent the fault. ??? Help please FoMoCo U.K. have been useless just blamed it on it being an "American" car. My Explorer was bought from a dealer in the U.K. and is right hand drive!! Thanks. Have had to call out vehicle recovery twice this year. In the open the key fob works up to 40 yards away.
 






jp450

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blackmore said:
I live in the U.K. and am experiencing the same fault caused by RF signals from the Ministry of Defence and police radio overpowering the key fob !!
Has any found a solution to the problem ? Can the system be switched off, overidden or modified in anyway to prevent the fault. ??? Help please FoMoCo U.K. have been useless just blamed it on it being an "American" car. My Explorer was bought from a dealer in the U.K. and is right hand drive!! Thanks. Have had to call out vehicle recovery twice this year. In the open the key fob works up to 40 yards away.

I am sure if you looked in your manual you will find the answer to your question. There is normaly a button under the dash that you will press to deactivate the system. That is what we do here in the US.
 






aldive

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jp450 said:
I am sure if you looked in your manual you will find the answer to your question. There is normaly a button under the dash that you will press to deactivate the system. That is what we do here in the US.

There is? Please explain.

Thanks ....
 






jp450

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I have a button under my dash to disable the immobiliser function of my system.
 












Abom

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But guys, in order for the keyfobs to be affected, they would have to be running on the same spectrum that the interferance is coming from.

Most cellular phone sites are either 800 MHz or 1900 MHz. Key fobs are usually down there in the 100 to 200 MHz range.

I have no idea what the stock Explorer key fob runs on for frequency, since I don't have remote locks. Someone who does, look on the back of the fob and see if it gives a MHz frequency.
 






tmanson

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Abom

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tmanson said:
The Fobs work at 315 MHz.

https://gullfoss2.fcc.gov/prod/oet/forms/blobs/retrieve.cgi?attachment_id=170549&native_or_pdf=pdf

I have the same intermitent problem. Seams to happen at Walmart alot. In the usa, 315 MHz is a universal band for Industrial, Scientific and Medical uses (key fobs, garage door openers, theft control devices, etc...). It is also used for Aeronautical & Maritime Radionavigation.

Ok, so we've established 315 MHz as the normal frequency. Now, in order for something to interfer with the keyfob, it would have to be on that same spectrum (or extememly close to it), and would have to be putting out more power.

Microwave ovens, just for say, operate at 890 MHz and higher, so we can rule those out.

Based on input power, a radio signal can travel through the air a certain distance. Let's take a CDMA cellular site for example. CDMA takes around 20 watts of continuous power. Let's assume the power input never changes. A site running on the 800 MHz spectrum will have a larger footprint (the distance the signal will travel from the cell site antennas) than a site running on the 1900 MHz spectrum. Most sites are 1900 MHz, simply because the 800 MHz spectrum is full and no longer being issued new licenses. (Except in the snowy white north where I live, hehe)

So using the same idea, say your key fob is right next to your door lock. The footprint of the key fob is very small, and as many of us know, at a short distance away, the fob's don't work anymore. So let's use the example of a garage door opener. Again, not a very large footprint. Let me make a crude but quick diagram.


(((((((<Explorer>)))))))


Let's say that the curly brackets are the footprint where the key fob is usable. Let's say, for argument's sake, that distance is 10 feet. Now let's say your neighbour has a remote garage door opener.

(((((((<Explorer>))))))) ((((((((((((((<Garage>))))))))))))))


Now, important to note is the power input we looked at earlier in the post. Garage door openers and remote door lock key fobs don't use the same power input. The key fob usually runs on 1.5 volts, normally a watch battery (really depends, but this is average), and the garage door opener runs on AA batteries (again, depends), and I have seen two batteries required in garage door openers, so now you're looking at 3 volts for that.

So if the garage door opener is twice as powerful as the Explorer key fob, then the RF (radio frequency) footprint of the garage door opener would be 20 feet. So in theory, your Explorer would have to be in that 20 foot radius in order to even have the possibility of the key fob being affected. And to add on top, the other device would have to be IN USE. A garage door opener doesn't emitt RF unless the button is being pressed.

So we can basically completely count out the small stuff like garage door openers, anti-theft devices, other car alarms and key fobs, etc. Government equipment like the above stated Aeronautical & Maritime Radionavigation, that could be a source of interference, but again, it would have to be on that exact same spectrum (or very close to it, we're talking like 315.11 and 315.15 being close together, 315.1 and 315.4 being completely independant).

If you want to test this out yourself, use your truck's FM radio. Tune to a station that's got good FM reception. Let's say it's 96.1 FM. Then tune to 96.3 FM. You can still hear the 96.1, but it's staticy and poor quality. This is when spectrum shifts / overlaps a bit. Now if there was another station that was licensed for that 96.3 FM, then the 96.1 would have to correct their issue so their RF doesn't overlap onto another spectrum (called isolating).

As I said in another thread, I'd grab a digital radio frequency scanner and go hunting on the 315 MHz band and see what else is out there. But interference shouldn't be THAT big of a concern, which would lead me to looking at other possibilities.
 






jp450

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Abom said:
Ok, so we've established 315 MHz as the normal frequency. Now, in order for something to interfer with the keyfob, it would have to be on that same spectrum (or extememly close to it), and would have to be putting out more power.

Not true.

If you take an "unsensitive" reciever or one with a loose front, much like the reciever for the keyless entry, and put any high power (As little as 1 watt can do under the proper circumstances) RF (radio frequency) source near it, it over drives the front end of the reciever and basicly all the reciever will hear is noise. A reciever that has all the necessary filters on it to prevent this can cost alot of money and for what it does the reciever in the keyless system that is installed is quite adequate for its purpose.


So basicly any source of RF is capable of preventing the reciever from hearing the weak key fob signal. Keep in mind that the poster with the problem is in the UK. They may not have the same frequency allocation that we have here in the states.

Here is a little experament that some may want to try. Take a scanner and program a NOAA weather frequency into it. Now with a FRS radio hold it up to the scanner that has the weather playing. Key up the mic. What happens? The scanner will stop recieving the weather recording. NOAA weather frequencys are in the 162 MHZ area. The FRS radio is in the 460 area and is at the most 1-2 watts. A scanner does not have a very tight front end on it and it will not hear the weather anymore. The same thing is happening with the fob and reciever.
 






tmanson

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What is an immobilizer?

Without a spectrum analyzer, the best method to prove interference is to go to a quieter RF area a see if it works (which it looks like a few have done). Field strength is inversely related to the square of the distance, or it gets weak very fast. So any smaller system, like Wal-Mart security system, would only affect you’re car if you were close to the building.

Now a Ministry of Defense and police radio system would require a greater separation. Sounds like you are sure it is the Police radio, so you’re system works when you get out of town?

The only thing we can easily mess with is the antenna. I do not know where it is even located, but radio waves do not like going through sheet metal. If the antenna could be located in a better position than it would receive the signals better. It would also receive the interfering signal, but hopefully the Fob signal would be more “on-frequency” and we would get more gain from the Fob than from the interference. This could probably be tested by just trying the remote from inside the car, as close to the receiver as possible.

Another option would be to build or buy a better antenna. A better antenna would hopefully be better tuned to 315 MHz and would receive the Fob better along with ignoring other frequencies.

http://www.okwelectronics.com/products/radio/antennas.htm

Any feed line (coax) attached to the receiver, for relocating the antenna, would have to be the correct impedance or the antenna would likely do no good. Most everything is 50 ohms, but not everything.

One more solution would be to build a passive band pass filter that would only allow 315 MHz through. Although you can filter out other frequencies, there is some loss at the target frequency also. There are also impedance matching considerations with this.

If you start tearing into you’re receiver there is always the possibly of f’n it up.

It might be easiest to disable the factory system and put in an aftermarket system that is on a different frequency or has a better receiver.

Here is a really technical discussion.
 






Abom

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jp450 said:
Not true.

If you take an "unsensitive" reciever or one with a loose front, much like the reciever for the keyless entry, and put any high power (As little as 1 watt can do under the proper circumstances) RF (radio frequency) source near it, it over drives the front end of the reciever and basicly all the reciever will hear is noise. A reciever that has all the necessary filters on it to prevent this can cost alot of money and for what it does the reciever in the keyless system that is installed is quite adequate for its purpose.


So basicly any source of RF is capable of preventing the reciever from hearing the weak key fob signal. Keep in mind that the poster with the problem is in the UK. They may not have the same frequency allocation that we have here in the states.

Here is a little experament that some may want to try. Take a scanner and program a NOAA weather frequency into it. Now with a FRS radio hold it up to the scanner that has the weather playing. Key up the mic. What happens? The scanner will stop recieving the weather recording. NOAA weather frequencys are in the 162 MHZ area. The FRS radio is in the 460 area and is at the most 1-2 watts. A scanner does not have a very tight front end on it and it will not hear the weather anymore. The same thing is happening with the fob and reciever.

Ok, well I suppose this all depends how strong the antenna is and how well the unit isolates it's own frequency. I was thinking in my head about Wilson cellular amplifiers vs CB radios, but now that I think about is, yes, what you say is true of small devices that weren't designed to filter everything but their own spectrum.

And yes, true that we don't know what is being used in the UK, I was only explaining using what we have here in North America. I still suggest using a digital scanner and investigating :)
 






blackmore

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immobiliser problem

I have a 1997 explorer with the same problem. Cant fix the problem but can avoid it. Before switching off the engine press the button on the remote and the immobiliser light on the dash should flash rapidly. if it does not the RF signal is probably being swamped by interference and you may have trouble restarting. Move to another location where the light flashes and you should be o.k. Cant promise it though, but I have tried it where I have been stranded before and the immolbiliser light DID NOT FLASH. Try it out !!!!
Neil
 






Highonlife

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I have a 1997 explorer with the same problem. Cant fix the problem but can avoid it. Before switching off the engine press the button on the remote and the immobiliser light on the dash should flash rapidly. if it does not the RF signal is probably being swamped by interference and you may have trouble restarting. Move to another location where the light flashes and you should be o.k. Cant promise it though, but I have tried it where I have been stranded before and the immolbiliser light DID NOT FLASH. Try it out !!!!
Neil


I'm having the same problem every time we goto a shopping area near a train station, Just cannot restart it. Have been recovered 4 times now and waited endless hours.
uk rhd.
will try this out as got nothing else.
wheres this cut off switch then?? and what do I need to do??

cheers for any help;)
 



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Doubt Incarnate

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my problem sort of dissolved itself, too bad i cant comment on any way to fix this. I'll just say it was the domestic spying program interfering.
 






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