Ha ha ha, Key FOB low battery but no warning on dash




I like traditional spin my key to start and most importantly able to do 1st and 2nd click key mechanical position with ease and highest accuracy without even looking at dash, from outside the car ( window opened ).
I can't remember if I replaced both Key FOB batteries or not when I got the car in 2018.
Assuming I did replace them which I doubt, that means my battery lasted 4 years, it was Panasonic.
If I did not replace it, that means 8 years it lasted.
I swap uses between the 2 keys usually once per year or every 2 years.
The key in use has 2.8V left and can't lock/unlock door wirelessly, but I still can unlock/lock door by touching the door handle...but sometime it did not work.
The spare key has basically a dead battery, 0.2 volts only LOL.
Could not get Panasonic, got Energizer instead but still fresh at 3.2 volts for both.
I wonder why I am not getting LOW BATTERY OF KEY FOB warning on the dash ?
Is it because I always insert the key into ignition key slot EIS and hence the RDF chip in the key which needs no battery power to operate the car, done its handshake with car computer and all is good ?
Regardless that I am on a KeyLess GO, even without the battery in key fob, I can start the car... so nice.
One question to those not using PUSH BUTTON START, because you don't like it or car version is older model without it..... do you get LOW BATTERY OF KEY FOB warning on the dash ?
Thanks




.Sister's W166 was draining the battery overnight unless she explicitly shut the Keyless module/computer down, i.e. two quick clicks when locking the car. FIX: remove the push button start and the draining went away. 4 years ago and counting
.Sister's W166 was draining the battery overnight unless she explicitly shut the Keyless module/computer down, i.e. two quick clicks when locking the car. FIX: remove the push button start and the draining went away. 4 years ago and counting
I'm not sure on the operation of the key in relation to keyless-go, but I'm assuming it doesn't monitor the key battery voltage if you're not using the push-button. I have fresh batteries in my keys, but it sure makes me want to try to see if this is the issue. I think I have a bad battery on my bench, I'll try to see if it gives me the warning with a dead battery and no push-button installed




I'm not sure on the operation of the key in relation to keyless-go, but I'm assuming it doesn't monitor the key battery voltage if you're not using the push-button. I have fresh batteries in my keys, but it sure makes me want to try to see if this is the issue. I think I have a bad battery on my bench, I'll try to see if it gives me the warning with a dead battery and no push-button installed




I'm not sure on the operation of the key in relation to keyless-go, but I'm assuming it doesn't monitor the key battery voltage if you're not using the push-button. I have fresh batteries in my keys, but it sure makes me want to try to see if this is the issue. I think I have a bad battery on my bench, I'll try to see if it gives me the warning with a dead battery and no push-button installed
I should have mentioned, the W166 was draining the main battery, not the keyfob's one.
Last edited by JCM_MB; Jan 24, 2023 at 10:49 AM.




Something interesting I found out while reading N73 for Juan PARK issue.
So the key when inserted uses no battery because it is wireless-ly being supplied power via induction coil.... aha. I initially thought simple RDF chip like key card entry to office/home.
Simple working of RDF https://en.wikipedia.org/wiki/Radio-...identification
No wonder the N73 has coils which I thought is the antenna .... LOL
So, NOT using push button I think is actually safer from car theft with 433Mhz radio sniffer, which the key FOB is using in wireless mode aka PUSH BUTTON.
My key FOB stated 433.92 Mhz frequency.
This frequency is a *****, so many devices uses this frequency. https://en.wikipedia.org/wiki/LPD433...PT%20countries.
I think if one is in area with very strong radio interferences and using push button aka wireless-ly, there could be times glitch may happen and resulted in a fraction of a second loss of drive authorization.
I wonder if tranny can go to PARK mode on its own ( when at low speed below 8 KM/H ) if LOST-COM occurred to key fob ?
===== ADD======
I think I should do some experiment.
Install my Push START button back, start engine and run it idling for some minutes , keep car in Neutral and then remove battery from/to key FOB, see if tranny goes to PARK
Last edited by S-Prihadi; Jan 24, 2023 at 02:26 PM.
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- Sleepless SAM, main battery drain
- Delayed unlock response
- Lotery ninja-kick trunk opening
- Moody ignition key & 3V coin cell
- Alarm active after unlocks
Do you wonder why...

the KeylessG controller
KGo is one of the module that makes frequent "battery reboots" an extremely good habit.
This module receivers are always partially powered to eventually ask F-SAM to wake up EIS for key authentication.

The Best of Mercedes & AMG








01. My driver may accidentally pocket the key when he goes home.
02. I do not like putting extra layer of radio work ( extra failure point ) to do something so important as key position 1-accessories , 2-ready to crank and most importantly CRANK-to-Start.
I also don't feel safe with push button when I am working at engine bay and key in no 2-ready to crank position when required by the task.
Key FOB Battery change is no issue even once a year or less.
I simply like more mechanical click-click control when and if I can enforce it.




The dealers change the battery for every oil service regardless of usage. At least that is what I saw when I took it for service early on, and to mimic I do the same. Once back from the Indy I replace both keyfob's batteries regardless of usage, they always sit side by side anyways.
Last edited by JCM_MB; Jan 25, 2023 at 11:11 AM.




Now in my case, the garage door is where all my keys get stored.
How far is good enough...?
- store your key in usual location
- walk to your driver door
- touch the handle inner surface
- listen: "quick clunk" under the car
- this is a wake up event.
If it takes a few tries to wakeup the main relay (clunk = latch) then it likely has sleep disorders (CAN B branch)





+1 :
this matches 100% my coin cell experience I consider standard in the bell-curve normal distribution sense.





Since this thread has more than 100 replies, I assume it has served the interests of several people as curious as me... https://mbworld.org/forums/e-class-w...-security.html
Bottom line... I bought the car in March, 2018. In the 5 years since, I've needed to replace the key fob batteries ONCE (within the last year, actually). Since I started getting the dashboard reminders mid 2022, I replaced the fob battery, and also started locking the car on exit. Silly to do this within a fully enclosed garage. But there are numerous threads about locking the car to shut down more of the standby electronics in the car. The car is never truly asleep.
Last edited by DFWdude; Jan 26, 2023 at 07:57 AM.




It is a very common failure for laptops to get into a non-booting state, and misdiagnosed as damaged, boot loop error, corrupted BIOS, piece of junk brand, etc. The symptom is: Fan spins for a moment after pressing the power button, and it shuts down regardless of battery charge.
That state is because the BIOS got corrupted due to a low voltage (auxiliary/buffer/standby) coin battery, I have seen laptops disposed of, or sold for 10's $ and they only needed a new coin battery. You should proactively change your coin battery before the device relying on them gets confused
My 2c.


