Key Fob frequency question
Thread Starter
Instructor
Joined: Jul 2008
Posts: 145
Likes: 2
From: Macon NC
Key Fob frequency question
I have a 98 and I have fiddled with my intermittent key fob for quite a while. Sometimes it works sometimes not so I decided to try and figure out what frequency it transmits. Does anyone have that information? I sent a note to the FCC but I don't expect much help. 
Thanks
Thanks
Thread Starter
Instructor
Joined: Jul 2008
Posts: 145
Likes: 2
From: Macon NC
I can't help with the frequency question but have you read through this thread?
http://forums.corvetteforum.com/c5-t...em-solved.html
http://forums.corvetteforum.com/c5-t...em-solved.html
I want to listen to the transmitter and hear the codes when I am at the vette. I suspect my problem is with the battery connections not making contact.
Safety Car
Joined: Jan 2001
Posts: 4,387
Likes: 691
From: Boise ID
Whoops! I had TPMS on my mind when researching but should be similar with the fobs.
Looking at one particular TPMS diagnostic tool’s specs, it shows 2 frequencies, 315 MHz and 433.92 MHz.
But.
Looking at Schrader 1997 patent #5,600,301, it states a frequency of 418MHz. Schrader 1999 patent #6,600,301 refers back to patent #5,600,301 for the frequency. As 8VETTE7 mentioned, the patent speaks of the encoding method used to transmit data.
Looking at one particular TPMS diagnostic tool’s specs, it shows 2 frequencies, 315 MHz and 433.92 MHz.
But.
Looking at Schrader 1997 patent #5,600,301, it states a frequency of 418MHz. Schrader 1999 patent #6,600,301 refers back to patent #5,600,301 for the frequency. As 8VETTE7 mentioned, the patent speaks of the encoding method used to transmit data.
Last edited by 87SAM; May 11, 2012 at 12:14 PM.
Tech Contributor
Joined: Jan 2007
Posts: 19,456
Likes: 1,165
From: Dyer, IN
Not to belabor the point but what good is knowing the transmit frequency going to do? Other function information is going to be encoded on the transmit to tell the receiver what it needs to send to the BCM and or PCM. ie tire pressures vs unlock vs lock etc. You would seemingly need to know that as well if you are trying to debug the transmissions.
Racer
Joined: Aug 2005
Posts: 388
Likes: 6
Yes and no. If he knows what frequncy the FOB transmits on, and has the equipment to monitor the strength, then you can establish a baseline...versus a new or other FOB. What happens after the receiver is only important if specific functions do not work......while others do.
I found using a spectrum analyzer with an antenna attached that the reason my euro vette's fob would intermittently not work at home was because something else was bang on the same frequency.
Thread Starter
Instructor
Joined: Jul 2008
Posts: 145
Likes: 2
From: Macon NC
Thanks for the frequerncy 315 MHz. I am looking for an intermittent when I am next to the vette and I can hear the code being transmitted on an AM receiver when I hold it close to the fob and all is working. I want to know which side is not working when it decides not to work. I am suspecting the battery to battery pads in the fob are breaking loose but then it seems I would loose sync in the rolling codes and I do have to resync but it does not loose the id. So maybe the third sub harmonic around 105 MHz might be in the FM broadcast band, I'll listen and learn...thanks
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Racer
Joined: Feb 2004
Posts: 359
Likes: 7
From: St. Paul MN
If you still have TPMS, are they ever intermittent? That may indicate an RFA issue (or a 14 year-old TPMS 
). Do you have one fob or two, and are they both having this issue? All year C5's are on 315 Mhz for both TPMS and key fob transmission which are received by the RFA. The differentiation between pre-01 C5's and 01+ are the data within the RF packet, but on the same frequency.
As cliff_ford found with his Euro fob, there are also lots of domestic devices that use 315 Mhz (garage door openers, security systems, other cars, etc), and you may just be overpowered by one of them. Does the fob have this symptom in multiple locations, or just one?
Two pieces in the communication chain to review, fob and receiver. Testing with a second fob would get to the bottom of one piece. Otherwise there are many folks who have "upgraded" from pre-01 RFA/fob/TPMS to the newer versions, and will often sell off the old components. A pre-01 RFA is probably $40.
Todd
). Do you have one fob or two, and are they both having this issue? All year C5's are on 315 Mhz for both TPMS and key fob transmission which are received by the RFA. The differentiation between pre-01 C5's and 01+ are the data within the RF packet, but on the same frequency. As cliff_ford found with his Euro fob, there are also lots of domestic devices that use 315 Mhz (garage door openers, security systems, other cars, etc), and you may just be overpowered by one of them. Does the fob have this symptom in multiple locations, or just one?
Two pieces in the communication chain to review, fob and receiver. Testing with a second fob would get to the bottom of one piece. Otherwise there are many folks who have "upgraded" from pre-01 RFA/fob/TPMS to the newer versions, and will often sell off the old components. A pre-01 RFA is probably $40.
Todd
Thread Starter
Instructor
Joined: Jul 2008
Posts: 145
Likes: 2
From: Macon NC
Thanks for the interest. I have TPMS and I replaced the modules when I bought my vette and they work every time. I only have one fob and I bought it when I bought the vette in 08. I think my intermittent operation in due to the fob and connections in the fob like the switches for the lock/unlock and trunk. I think a lot of fob's that get trashed are due to defective/dirty switches.
