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Thread: Shouldn't low FOB battery show up on Dash?

  1. #16
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    Most people*s lasted about a year. On average.

  2. #17
    Registered Member 7eregrine's Avatar

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    Quote Originally Posted by wlong01 View Post
    I don't know if I can buy the bad spot.
    It's happened to me at least a half dozen times in 3 years. Happens once upon entry and then not again for weeks.
    Battery going on 3 years and still original. I don't think 12 months is 'standard' for battery life.

    Beware Amazon batteries. I'm not buying those again. Bought 6 for my Volvo. Went through 5 of them in about 7 months. 6 should have lasted for years...
    Last edited by 7eregrine; 10-09-2019 at 09:11 AM.

  3. #18
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    Quote Originally Posted by 7eregrine View Post
    It's happened to me at least a half dozen times in 3 years. Happens once upon entry and then not again for weeks.
    Battery going on 3 years and still original. I don't think 12 months is 'standard' for battery life.

    Beware Amazon batteries. I'm not buying those again. Bought 6 for my Volvo. Went through 5 of them in about 7 months. 67 should have lasted for years...
    Beware Amazon anything. You have to be careful and make sure they're a trusted seller. Amazon is more like the middleman now, just takes the order and money and gives it to a remote seller. I've always had good luck with Amazon until recently. Ordered some cables and there was blatant false advertising. Luckily Amazon refunded my money.

  4. #19
    Registered Member 7eregrine's Avatar

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    Agree. Absolutely having more issues lately.
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  5. #20
    Registered Member Conrad 16.5's Avatar

    2016.5 CX-5 Grand Touring AWD titanium/black

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    Quote Originally Posted by 7eregrine View Post
    You get in the car with fob. You press button. Car looks for fob. Car detects faint signal. This is why it will work if you press it close to the button. It will never get to UTTERLY DEAD status unless you ignore it for weeks.

    Totally my theory, no facts included here.

    @OP: I've had this exact thing happen. It is probably just in a bad spot and didn't get the good detection on the signal. I think the car just didn't get a good 'look' at the key and assumes the battery is dead. Subsequent starts it 'sees' the key better.
    Close, but no cigar. (1995 called and asked me to explain it to you)

    There are two independent systems working in your fob.

    One uses battery power to 'broadcast' the signal to the car that it's ok to start once it 'sees' that the car is requesting authentication.

    The other system uses a proximity RFID chip in the fob that doesn't require battery power. That's why you have to place the fob close to the start switch. There's an induction coil near the switch that induces enough current in the fob to power the RFID chip.

    Don't believe me? Remove the battery from your fob and see if it works by placing it near the Start switch.
    Last edited by Conrad 16.5; 10-09-2019 at 09:19 AM.
    "Don't bother me with facts, Son. I've already made up my mind." -Foghorn Leghorn

  6. #21
    Registered Member 7eregrine's Avatar

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    Quote Originally Posted by Conrad 16.5 View Post
    Don't believe me? Remove the battery from your fob and see if it works by placing it near the Start switch.
    Why would I doubt you? I clearly stated I was guessing here.
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  7. #22
    Work in Progress sm1ke's Avatar
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    Quote Originally Posted by Avoidin Deer View Post
    But there's a "Battery Dead" warning. Is there a way to detect the key if its battery is dead? (Honest question, there's RFID technology that does not require a power source.) There's got to be a way to know there's a key present to tell you that its battery is dead.
    Does it actually say "Battery Dead"? If so, I could see that warning coming up when the fob no longer unlocks the door and you have to use the physical key. Maybe the Battery Dead warning is triggered by the RFID.

  8. #23
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    Use the fob to press the start button when it is low. I've went a week like that.

  9. #24
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    Quote Originally Posted by Conrad 16.5 View Post
    Close, but no cigar. (1995 called and asked me to explain it to you)

    There are two independent systems working in your fob.

    One uses battery power to 'broadcast' the signal to the car that it's ok to start once it 'sees' that the car is requesting authentication.

    The other system uses a proximity RFID chip in the fob that doesn't require battery power.
    That's what I was questioning earlier. So you can get a warning light saying Fob Battery Dead because the RFID chip tells the system that there's a fob nearby.

  10. #25
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    Quote Originally Posted by sm1ke View Post
    Does it actually say "Battery Dead"? If so, I could see that warning coming up when the fob no longer unlocks the door and you have to use the physical key. Maybe the Battery Dead warning is triggered by the RFID.
    Yeh, it says "Battery Dead" in the 2019 manual.

    I'm thinking what you said: RFID sees a key is there, but it's not transmitting. Except RFID does not have that great a range, but I can't think of anything else.

  11. #26
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    Think I figured out the problem with the fob.

    Went out this morning, fob in pocket, put my foot on the brake, no light on start button. Took the fob out, put it right next to the start button - nothing Then I noticed the brake was locked up tight, pressed the brake hard and felt something like a contact switch, then the green light came on. For some reason in the morning the brake pedal is locked tight.
    I'm used to just putting my foot on the brake with light pressure. It's that way all during the day but when it sits overnight the brake gets really tight requiring a lot of pressure to move the pedal. Once it starts the brake feels normal.

  12. #27
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    Now you may have another problem, huh?

    I've got a Reserve. I use my Parking Brake all the time, and have never had that issue. I'm retired and the car has sat for a couple of days without being driven.

    I wonder what's going on...maybe something with the power assist unit?

  13. #28
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    OP: Try this next time you get in your car first thing in the morning: don't press the brake pedal and push the ignition switch. If the key fob is being detected, the car won't start but the car will go into accessory mode. If nothing happens, the fob isn't being detected.

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