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Key Fob Battery Replacement = Dead Key

Posted: Sat Apr 24, 2021 12:37 pm
by scottbrooks
Hi,

I have a 2016 SV that has mostly been reliable. I just replaced the battery in the fob and now it is dead. I tried a couple of the reset sequences published on dealer sites but (a) they are for cars with a key socket and (b) it didn't work. The dealer wants $80 + tax to reset the key.

Any ideas on how to reprogram this at home?


Unrelated: I can't get the car to register more than 90 miles range with a full charge. Common?

Re: Key Fob Battery Replacement = Dead Key

Posted: Sat Apr 24, 2021 5:13 pm
by GerryAZ
There is no need to "reset" anything when just replacing the fob battery. If the fob was working before replacing the battery, then you have a defective battery, battery installed wrong, or you damaged the circuit board in the fob by putting the wrong battery in it. Try removing the battery from the fob and then holding the fob directly against the start button of the car, If the car starts, then replacing the fob battery with a good one of the correct size may fix it.

Re: Key Fob Battery Replacement = Dead Key

Posted: Sat Apr 24, 2021 6:17 pm
by scottbrooks
Thanks. This is a weird one...

1) I tested the new battery with my multimeter. It is good.
2) The fob is recognized by the car and works in the dead battery proximity start process
3) It was in the correct way, + side down
4) It is the correct 2025 battery

I swapped in the old battery, also a 2025 and it works. I don't have a caliper but I visually inspected the two batteries. It looks like the new one is maybe a hair thinner so I gently bent the tabs up. Not so much! I popped the old battery in and it works fine, but the level is low.

Any ideas?

Re: Key Fob Battery Replacement = Dead Key

Posted: Sat Apr 24, 2021 7:24 pm
by goldbrick
The only thing I can suggest is try another (new) battery. Maybe a different brand.

Re: Key Fob Battery Replacement = Dead Key

Posted: Sat Apr 24, 2021 8:59 pm
by GerryAZ
Try another new 2025 battery. Digital multimeters have very high input impedance so a defective battery can test OK (show normal voltage for a new battery), but not be able to deliver current.

Re: Key Fob Battery Replacement = Dead Key

Posted: Sat Apr 24, 2021 9:56 pm
by LeftieBiker
GerryAZ wrote:
Sat Apr 24, 2021 8:59 pm
Try another new 2025 battery. Digital multimeters have very high input impedance so a defective battery can test OK (show normal voltage for a new battery), but not be able to deliver current.
Yes, and there are so many Chinese counterfeit batteries being sold that it's harder to find a real one than you would think.

Re: Key Fob Battery Replacement = Dead Key

Posted: Sun Apr 25, 2021 5:58 am
by Stanton
GerryAZ wrote:
Sat Apr 24, 2021 8:59 pm
Try another new 2025 battery. Digital multimeters have very high input impedance so a defective battery can test OK (show normal voltage for a new battery), but not be able to deliver current.
^^^ THIS
I just replaced my key fob battery with what was (supposed to be) a new battery...and no joy.
BTW, you can fit a 2032 in our key fobs if you have any laying around...and it will work.

Re: Key Fob Battery Replacement = Dead Key

Posted: Sun Apr 25, 2021 10:16 am
by lorenfb
GerryAZ wrote:
Sat Apr 24, 2021 8:59 pm
Try another new 2025 battery. Digital multimeters have very high input impedance so a defective battery can test OK (show normal voltage for a new battery), but not be able to deliver current.
An alternate battery test for small "coin" type batteries, e.g. 2025 when using a multimeter, is to use the ammeter scale (highest setting 1st)
to do a basic load test. A good 2025 should provide about 100-200 milliamps.

Re: Key Fob Battery Replacement = Dead Key

Posted: Sun Apr 25, 2021 2:14 pm
by jjeff
lorenfb wrote:
Sun Apr 25, 2021 10:16 am
GerryAZ wrote:
Sat Apr 24, 2021 8:59 pm
Try another new 2025 battery. Digital multimeters have very high input impedance so a defective battery can test OK (show normal voltage for a new battery), but not be able to deliver current.
An alternate battery test for small "coin" type batteries, e.g. 2025 when using a multimeter, is to use the ammeter scale (highest setting 1st)
to do a basic load test. A good 2025 should provide about 100-200 milliamps.
Not sure I understand why you are saying, do you mean to short circuit the battery with an ammeter and shorted out it should show 100-200ma? if so I guess I've never done that, I for sure wouldn't want to do it with a higher current battery but may be ok with something as tiny as a coin battery?
Again if I understand you correctly, what should a 2032 battery be capable for ma? I'd assume more than a 2025 as it's larger.

Re: Key Fob Battery Replacement = Dead Key

Posted: Sun Apr 25, 2021 2:45 pm
by LeftieBiker
You wouldn't be shorting the battery - you'd be placing a substantial load on it from the resistor in the ammeter.