[dhlairbusb4]

When I bought the car, only one key fob would start the car, but both would unlock/lock. New battery in both fobs, no change.
For no reason, the fob in question started working, I was trying it out before shipping it to SOS diagnostics. I thought I was
back in business with two keys that worked!!! Well, this little gremlin likes to play, and I am his unwilling partner so to speak.
After a month or two, using the problematic fob, it failed again... and yes... I was away from home with out the backup fob.
Took it to the MB dealer, they reprogramed it, it worked great... for 24 hours, then back to its unreliable self again.
So, after another couple of months, with the bad fob left in the car so I could randomly try it... it worked!!! I am using it again
but this time with the second fob always available.
I have removed the fob guts, looked for dirt, junk etc... blown it out and cleaned the all the rubber contacts... but still find
it strange this gremlin likes to keep messing with me.
Sending both fobs, the Sam, and ECU to SOS seems like the next step, when it fails again...!
Does anyone have any idea what could be the problem with this key fob? I am fortunate my backup works fine, and hope to
keep it that way.

 

[Bob Denman]

Ouch! I don't envy you.
Good luck!

 

[jzchen]

With all the effort, I think you have an unreliable fob. I suggest getting a replacement.

Sent from my moto g(7) power using Tapatalk

 

[dhlairbusb4]

Bob, are you suggesting I buy an I-Robot, maybe that would work? Not only would it hopefully keep my fob working, but it could
run around in the back and keep my carpet clean!!!

 

[dhlairbusb4]

JZ Yeah, that will probably be the next step, when it fails again. Its just having to plan parking the car for a week or so
to allow for mailing the components to SOS for the repair/replace, and then reinstalling such when it comes back.

 

[toaster]

When I bought the car, only one key fob would start the car, but both would unlock/lock. New battery in both fobs, no change.
For no reason, the fob in question started working, I was trying it out before shipping it to SOS diagnostics. I thought I was
back in business with two keys that worked!!! Well, this little gremlin likes to play, and I am his unwilling partner so to speak.
After a month or two, using the problematic fob, it failed again... and yes... I was away from home with out the backup fob.
Took it to the MB dealer, they reprogramed it, it worked great... for 24 hours, then back to its unreliable self again.
So, after another couple of months, with the bad fob left in the car so I could randomly try it... it worked!!! I am using it again
but this time with the second fob always available.
I have removed the fob guts, looked for dirt, junk etc... blown it out and cleaned the all the rubber contacts... but still find
it strange this gremlin likes to keep messing with me.
Sending both fobs, the Sam, and ECU to SOS seems like the next step, when it fails again...!
Does anyone have any idea what could be the problem with this key fob? I am fortunate my backup works fine, and hope to
keep it that way.

I too have an intermittent key, but mine is the remote lock/unlock function which stopped working for a while only to once again work. Both would start the car.

A little bit of information on the functionality of these keys:

- The key has a low frequency transponder for starting the car and a high frequency one (315MHz) for remote lock/unlock.

- The low frequency one is powered up by a coil in the ignition switch and does not require the key fob battery.

- The high frequency one requires a good key fob battery to transmit its signal for remote lock/unlock.

- The key 'might' be locked to the vehicle. I do not know if this is true, but the IC used in the key has this capability. If smart has implemented this, a used key will not be able to be programed to the car unless it has first been restored to a 'new' state. This is not something the dealer can do, but possibly a firm like SOS Diagnostics.

Aftermarket keys are available for reasonable prices...if only the 10-minute dealer programming was reasonable as well.

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~toaster

 

[dhlairbusb4]

T Sounds like we have the same/opposite problems. If I do send this to SOS in the future, I hope that is the end of the gremlin!
I did have problems with lock/unlock activating with the key in my pocked. I tried to sand down the rubber thingies (technical term) with a
nail file, and it worked... although I had to do this a couple of times. So no more unwanted locking/unlocking for me!

 

[toaster]

T Sounds like we have the same/opposite problems. If I do send this to SOS in the future, I hope that is the end of the gremlin!
I did have problems with lock/unlock activating with the key in my pocked. I tried to sand down the rubber thingies (technical term) with a
nail file, and it worked... although I had to do this a couple of times. So no more unwanted locking/unlocking for me!

The smart key fob uses mechanical switches. The rubber buttons just press on these switches. I understand you may be trying to prevent their slight protrusion from activating the switch.

Was it the lock or unlock which was falsely activating?

If the button was not actually pressed, then I'd suspect the switch on the pcb to be faulty or possibly some contaminants may have entered the switch.

~toaster

 

[Bob Denman]

The fob in question might just have a small break in the "wiring"
(or whatever it is in there; that makes the magic happen...)
Tiny enough to cause an intermittent loss of function, and be even tougher to find
Throw it away, and get yourself a replacement.

 

[jzchen]

JZ Yeah, that will probably be the next step, when it fails again. Its just having to plan parking the car for a week or so
to allow for mailing the components to SOS for the repair/replace, and then reinstalling such when it comes back.

Is that cheaper than getting a new key through the dealer? When my mother was robbed with her Mercedes key in her purse I went and got replacement everything and they reprogrammed the remaining key, erased the missing one, and programmed the new one...

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[twcom]

Could the original post key with key fob that works all the time, really be a key blade issue.
Key may have been cut slightly off and lines up in the cylinder just right at times. I have several sets of keys for my SUV, all keys and key fobs work but one key wont manually unlock the doors and requires finesse to start the car.
When I look closely at that key its visible that it is not cut the same as the others on one side.
.
Back to the original post, "dhlairbus b4" may get away with just a new blade cut from the working Key. Take a real hard look at the two key blades. After all the Fob is already programmed.

 

[albertlastsmart]

I had a key fob that would start the car,but NOT unlock/lock the doors/rear hatch. Somehow in changing the
battery in the fob,the contacts to the battery got compressed. Bent the contacts back up to contact the battery.
Works like new again........................

 

[Bob Denman]

How often should the keyfob battery be replaced?

 

[jwight]

How often should the keyfob battery be replaced?

When the battery gets low, the car will flash its lights nine times (yes, its true!) - letting you know the battery needs to be replaced. Covered in the owners manual.

 

[sokoloff]

The annual maintenance sheet indicates that the battery should be replaced yearly. However, that's pretty much as a CYA/profit for the dealer. If you DIY, replace it when needed. I'm going on six years on mine. Might be time to do a preemptive replacement. Thanks for reminding me.

Len

 

[Bob Denman]

Mine are four years ikd: I guess it's time to find some replacement batteries...
Thanks!

 

[sokoloff]

Takes CR2016. I've got them on hand. Guess maybe it's time to think about using them.

Len

 

[Bob Denman]

CR2016? Got it!
After you change them: do you have to preform any reprogramming tasks?
(I don't have a manual...)

 

[sokoloff]

CR2016? Got it!
After you change them: do you have to preform any reprogramming tasks?
(I don't have a manual...)

Nope, just plug and play.

Len

 

[khlam]

Takes CR2016. I've got them on hand. Guess maybe it's time to think about using them.

Len

FYI, I have a 2016 Fortwo and my key fob takes one CR2032 battery