Key fob issue?
07-30-2014, 01:12 PM
#21
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The system is designed so you can get into the car even if the battery in the fob is completely dead. When you touch the button on the door, the car sends out a signal to see if the fob is nearby. The radio waves in that signal induce a small current in part of the radio frequency device so that it can transmit a reply (I'm here.) without using any power from the fob battery (It's dead.), and the car door opens.
The radio frequency device is much like the security tags they put on high-dollar merchandise that set off an alarm at the store exit. They have no battery, and they only work for short distances because the signal they put out is very weak.
If the fob battery was needed to open the door, you'd have to get it replaced before you could even get into the car, and that could be an unacceptable inconvenience to most people.
The radio frequency device is much like the security tags they put on high-dollar merchandise that set off an alarm at the store exit. They have no battery, and they only work for short distances because the signal they put out is very weak.
If the fob battery was needed to open the door, you'd have to get it replaced before you could even get into the car, and that could be an unacceptable inconvenience to most people.
Tell you what.. later today when I have some time, I'll remove the battery from my FOB and try to enter the car.
Care to bet (to St Jude) as to whether it works or not?
07-30-2014, 01:44 PM
#22
Melting Slicks
Thread Starter
OK, here's the latest. I got home with the new battery in the fob and clicked it to unlock and the lights came on as usual. So far, so good. I assumed all was OK so never drove it last night. Thought I would take it to work today and same issue; the 'no fob detected' shows up on the DIC and the car starts when the fob is inserted in the column. I drove it to work and just came back from lunch-same deal. I don't know if the new fob battery is dead already due it constantly searching (as I alluded to earlier) or some other problem. I'll try the second fob tonight and hopefully that one still works. I have a dealer oil change scheduled for Sat. so I'll see if they have any resolution. I doubt they will stock a new fob if that's what's required. I leave next Thursday for the races at Road America and definitely want this corrected before I hit the road...
Will the car continue to start (like forever) using the fob-into-slot method even though the fob battery is dead? If that's the case, as long as you have a fob you're not going to be stranded but if not you're screwed.
I believe 'welder guy' is correct; my car was locked but touching the door button opened it even though the fob battery is supposedly dead.
It was in my pocket, so the proximity idea would seem logical. I agree, having a dead fob battery prohibiting you from entering the car would not be acceptable to most people even though there is the key/hatch method.
Will the car continue to start (like forever) using the fob-into-slot method even though the fob battery is dead? If that's the case, as long as you have a fob you're not going to be stranded but if not you're screwed.
I believe 'welder guy' is correct; my car was locked but touching the door button opened it even though the fob battery is supposedly dead.
It was in my pocket, so the proximity idea would seem logical. I agree, having a dead fob battery prohibiting you from entering the car would not be acceptable to most people even though there is the key/hatch method.
07-30-2014, 02:13 PM
#23
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UPDATE after testing my (educated) theory
So, I removed the battery from my FOB and tried to open both doors and the hatch of my coupe. As I fully expected - no battery, no workie. However, placing the battery-less FOB in the steering wheel slot DOES allow the car to start. (UPDATE: I am not sure if this worked because the door was previously unlocked by authorized means and therefore the car would start regardless - such as in the case of driving off and leaving your FOB at home yet the C7 will allow a restart without a FOB). I will have to test this later on as well)
The concept of the FOB being like an RFID chip is flawed in that RFID requires very close coupling in order to work (I won't go into the math of power density but suffice it to say that the amount of RF/magnetic energy needed to transfer any meaningful amount of power from one place to another becomes more difficult on a massive scale (for those interested in the formula -
Friis_transmission_equation)
Of course, this also means that by placing the FOB in the steering wheel might be able to assist a weak FOB battery as the FOB would be close-coupled with the car's systems (I assume an antenna or coil of some sort) and enough power could be coupled into the FOB under this circumstance.
And for what it's worth, as part of what I do for a living is RF related, I have some specialized test equipment (in the case of this test, a spectrum analyzer) and can verify #1 below.
Anyway, I hope I was able to put the various FOB theories to bed
1) The FOB does NOT periodically send out a signal but rather waits until either one of the buttons is pushed or it is polled by the C7
2) The FOB battery is indeed required in order for the FOB to unlock the door and start the car, unless placed in the steering wheel pocket.
The concept of the FOB being like an RFID chip is flawed in that RFID requires very close coupling in order to work (I won't go into the math of power density but suffice it to say that the amount of RF/magnetic energy needed to transfer any meaningful amount of power from one place to another becomes more difficult on a massive scale (for those interested in the formula -
Friis_transmission_equation)Of course, this also means that by placing the FOB in the steering wheel might be able to assist a weak FOB battery as the FOB would be close-coupled with the car's systems (I assume an antenna or coil of some sort) and enough power could be coupled into the FOB under this circumstance.
And for what it's worth, as part of what I do for a living is RF related, I have some specialized test equipment (in the case of this test, a spectrum analyzer) and can verify #1 below.
Anyway, I hope I was able to put the various FOB theories to bed
1) The FOB does NOT periodically send out a signal but rather waits until either one of the buttons is pushed or it is polled by the C7
2) The FOB battery is indeed required in order for the FOB to unlock the door and start the car, unless placed in the steering wheel pocket.
Last edited by KenHorse; 07-30-2014 at 02:38 PM.
07-30-2014, 02:33 PM
#24
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The system is designed so you can get into the car even if the battery in the fob is completely dead. When you touch the button on the door, the car sends out a signal to see if the fob is nearby. The radio waves in that signal induce a small current in part of the radio frequency device so that it can transmit a reply (I'm here.) without using any power from the fob battery (It's dead.), and the car door opens.
The radio frequency device is much like the security tags they put on high-dollar merchandise that set off an alarm at the store exit. They have no battery, and they only work for short distances because the signal they put out is very weak.
If the fob battery was needed to open the door, you'd have to get it replaced before you could even get into the car, and that could be an unacceptable inconvenience to most people.
The radio frequency device is much like the security tags they put on high-dollar merchandise that set off an alarm at the store exit. They have no battery, and they only work for short distances because the signal they put out is very weak.
If the fob battery was needed to open the door, you'd have to get it replaced before you could even get into the car, and that could be an unacceptable inconvenience to most people.
I'm sorry but this is wrong.
You are saying that you can open the door with a dead RKE battery? NFW. Try it. Take the battery out of the RKE and try to open your door. I'll wait..........
You MUST have a battery in the RKE that is capable of transmitting a signal to the car to identify the RKE as "Authorized". Without the battery in the RKE, the only way to get in the car is the key in the rear hatch/trunk to get it open and pull the handle to open the door. You can then place the dead battery RKE in to the slot in the steering column and start the car. The system is designed to let you start the car with a dead RKE battery by using the slot and the "induction" of which you speak can occur but ONLY in the slot.
Elmer
Last edited by eboggs_jkvl; 07-30-2014 at 02:46 PM.
07-30-2014, 02:38 PM
#25
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OK, here's the latest. I got home with the new battery in the fob and clicked it to unlock and the lights came on as usual. So far, so good. I assumed all was OK so never drove it last night. Thought I would take it to work today and same issue; the 'no fob detected' shows up on the DIC and the car starts when the fob is inserted in the column. I drove it to work and just came back from lunch-same deal. I don't know if the new fob battery is dead already due it constantly searching (as I alluded to earlier) or some other problem. I'll try the second fob tonight and hopefully that one still works. I have a dealer oil change scheduled for Sat. so I'll see if they have any resolution. I doubt they will stock a new fob if that's what's required. I leave next Thursday for the races at Road America and definitely want this corrected before I hit the road...
Will the car continue to start (like forever) using the fob-into-slot method even though the fob battery is dead? If that's the case, as long as you have a fob you're not going to be stranded but if not you're screwed.
I believe 'welder guy' is correct; my car was locked but touching the door button opened it even though the fob battery is supposedly dead.
It was in my pocket, so the proximity idea would seem logical. I agree, having a dead fob battery prohibiting you from entering the car would not be acceptable to most people even though there is the key/hatch method.
Will the car continue to start (like forever) using the fob-into-slot method even though the fob battery is dead? If that's the case, as long as you have a fob you're not going to be stranded but if not you're screwed.
I believe 'welder guy' is correct; my car was locked but touching the door button opened it even though the fob battery is supposedly dead.
It was in my pocket, so the proximity idea would seem logical. I agree, having a dead fob battery prohibiting you from entering the car would not be acceptable to most people even though there is the key/hatch method.
If the second RKE works, you have killed your other RKE in the washing machine. It will need to be replaced and programmed. There is a thread in the FAQs on the C7s that will tell you how to program it.
Elmer
Last edited by eboggs_jkvl; 07-30-2014 at 02:50 PM.
07-30-2014, 03:18 PM
#26
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So why did the old push button FOB's batteries last "forever" and with these new fangled ones they last maybe if your lucky 2 years? What changed with the modern version to run the batteries down quicker?
07-30-2014, 03:23 PM
#27
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St. Jude Donor '11-'12-'13, '16-'17-'18
I can't attest to battery life (yet) but perhaps these newer FOBs draw more current? The 2032 battery used is rated at roughly 200 mAh (milliamp hours), FWIW.....
07-30-2014, 03:29 PM
#28
Melting Slicks
Thread Starter
You missed the detail on my original post; the fob was in the laundry basket waiting to be laundered-it was never put in the washer. If that happened I would totally expect it to be toast but it was just in a shorts pocket in a pile of other clothes-that's why I'm wondering what happened.
07-30-2014, 03:51 PM
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07-30-2014, 04:24 PM
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You missed the detail on my original post; the fob was in the laundry basket waiting to be laundered-it was never put in the washer. If that happened I would totally expect it to be toast but it was just in a shorts pocket in a pile of other clothes-that's why I'm wondering what happened.
Elmer
07-30-2014, 07:53 PM
#32
My car has always started fine with the main key fob that was supplied. The second one had never been used and was in a drawer. Over the weekend I planned to use the car for a couple of errands and when it wasn't in the usual spot I remembered the 'main' fob was still in the shorts I had worn at Car Craft the following Sunday. Rather than go through the laundry basket (no it hadn't gone through the wash) I just grabbed the second fob and drove off. When I returned I retrieved the original fob and later wanted to back the car out for some detailing. I got a "no fob detected" message.
I was able to start it by inserting the fob into the slot by the steering wheel but that's the only way it will start now using that fob. Does it need to be reprogrammed or something? My car is an early one (#307) built in late August so the fobs are almost a year old-maybe a bad battery? Any suggestions before I bring it to the dealer?
I was able to start it by inserting the fob into the slot by the steering wheel but that's the only way it will start now using that fob. Does it need to be reprogrammed or something? My car is an early one (#307) built in late August so the fobs are almost a year old-maybe a bad battery? Any suggestions before I bring it to the dealer?
07-30-2014, 10:56 PM
#34
22 Hypersonic Grey HTC
Tonight for the first time the trunk on my coupe didn't pop open when I held down the button on the FOB.
I hope it's just a one-time-thing...
I love this car!
07-31-2014, 05:22 AM
#35
had something like that happen on mine and it worked .but yours almost sounds like a batt, prob, too.
also those work on r.f. signals reg. start on one and remote start on another. some things will interfere with those .
mine wouldn't work one day because i was parked in just the wrong place .
anyway if the above dosen't work take the batt ,out of the good fob. and put it in the bad one see if its the batt.
if you do have to have it repro. it's no big deal . let us know the out come good luck
also those work on r.f. signals reg. start on one and remote start on another. some things will interfere with those .
mine wouldn't work one day because i was parked in just the wrong place .
anyway if the above dosen't work take the batt ,out of the good fob. and put it in the bad one see if its the batt.
if you do have to have it repro. it's no big deal . let us know the out come good luck
07-31-2014, 11:25 AM
#36
Melting Slicks
Thread Starter
I drove it to work today using the 'good' fob and will hold off on any other 'experimenting' at this point and let the dealer check it out on Saturday. I did try the remote start with the suspect fob and nothing...
07-31-2014, 11:50 AM
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Either:
- The battery is bad
- The battery is inserted incorrectly
- The battery is not making proper contact
- The RKE is malfunctioning
Elmer
07-31-2014, 11:59 AM
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I guess this would qualify as a malfunction but the other possibility is that the FOB is coded wrong (not "paired" with the car)
07-31-2014, 12:20 PM
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07-31-2014, 04:34 PM
#40
Melting Slicks
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The problem I'm having is with the original fob that I've used since last October when I took delivery, so it should not be a question of being paired with the car. The second fob that I pulled out of the drawer and used today works fine. Something caused the first one to crap out and it appears to be more than a battery situation. I'm still thinking back to the tech at Batteries + comments after replacing the battery that when he tested it there was evidence of it sending a constant search/signal even though the vehicle was 12 miles away.