Shouldn't low FOB battery show up on Dash?

wlong01

Patron
:
2019 CX5 Reserve AWD
For the last 4 days when I went to start the car in the morning, nothing, no green, orange, red on the start button. When I take the FOB and wave it around close to the start button it will eventually turn green and start.
The rest of the day it works fine, even when it's in my pocket.

I thought I would get a low battery warning on the dash if indeed the battery is low.
Don't have access to the other FOB right now but will check it when my wife returns from out of town.

Wonder if these FOB batteries sit around or if the dealer refreshes them when you take delivery of the vehicle.
 

shadonoz

SkyActiv Member
Contributor
:
State of Jefferson
:
2017 CX-5 GT AWD+
For the last 4 days when I went to start the car in the morning, nothing, no green, orange, red on the start button. When I take the FOB and wave it around close to the start button it will eventually turn green and start.
The rest of the day it works fine, even when it's in my pocket.

I thought I would get a low battery warning on the dash if indeed the battery is low.
Don't have access to the other FOB right now but will check it when my wife returns from out of town.

Wonder if these FOB batteries sit around or if the dealer refreshes them when you take delivery of the vehicle.
You should. I've gotten the warning on both of my original batteries. One after about 18 months, the next after about 6 month [2 years after delivery]. The warning came before any malfunctions.
They're standard cr2025s. They can't be recharged, and I'm sure the dealer doesn't replace them when new.
Since you have a 19, it seems too soon for the battery to fail, but always check that first!
 

Avoidin Deer

Zoom Zoom, baby
Contributor
:
Central Virginia
:
2019 CX-5 Reserve
The thing that makes no sense to me is the Key Warning Indicator is supposed to be white if the FOB battery is dead. But how would it even know the FOB is in the car if the battery in it is dead?
 

7eregrine

The man, the myth, the legend
:
Land of Cleve
:
2016.5 CX5
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.
 
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Avoidin Deer

Zoom Zoom, baby
Contributor
:
Central Virginia
:
2019 CX-5 Reserve
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.
So in theory, I should be able to get into the car with no FOB on me, press the button, and the FOB Battery indicator should say Dead Battery.

I'll have to give it a try.
 

Avoidin Deer

Zoom Zoom, baby
Contributor
:
Central Virginia
:
2019 CX-5 Reserve
How long does it take a new fob to drain to 0%?
It would likely depend on how often you push the buttons on it.

I have my doors automatically "Walk Away Lock," so I never use the FOB's transmitter to lock/unlock them or to open the hatch. My battery is likely to last the longest under those conditions.
 

sm1ke

Work In Progress..
Moderator
Contributor
:
Canada
:
'18 CX-9 Signature
If my key fob is running low on battery, I get a warning message in the instrument cluster when I turn off the car.

It's always good to have a few CR2025 batteries on hand. They're like $1 for a pack of 3. Or you can get a pack of 10 Panasonic batteries for $5 on amazon.
 

sm1ke

Work In Progress..
Moderator
Contributor
:
Canada
:
'18 CX-9 Signature
So in theory, I should be able to get into the car with no FOB on me, press the button, and the FOB Battery indicator should say Dead Battery.

I'll have to give it a try.
I think you'd get a "Key Not Detected" error. The car needs to be able to detect the key in order to determine if the battery is low.
 

shadonoz

SkyActiv Member
Contributor
:
State of Jefferson
:
2017 CX-5 GT AWD+
So in theory, I should be able to get into the car with no FOB on me, press the button, and the FOB Battery indicator should say Dead Battery.

I'll have to give it a try.
I think you'd get a "Key Not Detected" error. The car needs to be able to detect the key in order to determine if the battery is low.
Mine first says "key not detected" and then "low battery".

So it does NOT need to detect the key. If it doesn't detect it, it assumes the battery might be low.
 

wlong01

Patron
:
2019 CX5 Reserve AWD
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.
I don't know if I can buy the bad spot. I've had my 16 for 4 yrs and wear the same type of pants/shorts and it has never missed. Plus on the 19 it detects the FOB since it lets me unlock the drivers door with the FOB in my pants pocket. I will change the battery when I'm able to and go from there

It's weird because I went out this morning and had trouble. Went out two times after that later and no problem. Same pants, FOB in same pocket.
 

Avoidin Deer

Zoom Zoom, baby
Contributor
:
Central Virginia
:
2019 CX-5 Reserve
Change your battery and see if that fixes it.

If not, use the other fob for a while and start to narrow down the problem point.

ps: Apologies for using upper case letters for fob. It's a noun, not an acronym for Free On Board. Five years into retirement and I just can't break the habit.
 

ColoradoDriver

Gen-1 Kodo Design
Contributor
:
Denver, CO
:
2014 CX-5 Touring
My first FOB battery lasted 3 years. I probably prematurely replaced it again a couple years after when I thought it was dead again, but ended up being a switch under the gated shifted in my 2014.
 

Avoidin Deer

Zoom Zoom, baby
Contributor
:
Central Virginia
:
2019 CX-5 Reserve
I think you'd get a "Key Not Detected" error. The car needs to be able to detect the key in order to determine if the battery is low.
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.
 

shadonoz

SkyActiv Member
Contributor
:
State of Jefferson
:
2017 CX-5 GT AWD+
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.
Guess you didn't see this, or didn't understand the implications.

Mine first says "key not detected" and then "low battery".

So it does NOT need to detect the key. If it doesn't detect it, it assumes the battery might be low.
It gives the low battery warning when the battery reaches a voltage threshold, long before it ever goes dead.
 

7eregrine

The man, the myth, the legend
:
Land of Cleve
:
2016.5 CX5
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...
 
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wlong01

Patron
:
2019 CX5 Reserve AWD
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.
 
:
2016.5 CX-5 GT AWD titanium/black 2016 Miata Club ST MT white
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.
 
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