I'm sure we have all experienced the frustration of being in a hurry, sit in the car, hit the start button and then realize "Dang! I left my key on the key hook in the house!!"

Well, my problem is worse.

Several times over the past month I got to my destination (work, grocery store, car wash, Wendy's) and when I went inside I could not lock my doors because I did not have my key with me!!

How I have been so lucky that my car still started, I don't know. But it is only a matter of time before I will be stuck somewhere. As we all know, it will be when I am about 100 (or more) miles from home. It is not consistent. I have still been unable to start my car on occasion sans key.

Obviously this is 100% a user error problem as if I were responsible enough to keep my keys with me this would not be a problem. However, if anyone has run across this and discovered it is something that can be fixed, feel free to share.

 

Do you happen to have a work-bag, that contains your spare key ? If so, then that will account for why the car started, without the key in your pocket.

 

Are you leaving your car unlocked? Unless your key hook is right on the wall next to your car or something how are you getting into the car without the key on you in the first place?

 

That has never happened to me. The car won't start if the key is not inside the vehicle. You've got to have your spare key somewhere in the car, which is how you can start it. You can technically leave the key behind once the engine is running, but you'll get a warning in the instrument cluster that it can't detect the key anymore.

 

Give me SOME credit! The first time it happened, I "knew" the key had to be in my car somewhere. I searched under the seats, the trunk, glove box, armrest, etc. I finally called home and asked the wife to check and sure enough, she confirmed both keys were hanging up.

 

I don't lock my car in my garage. It is usually when I arrive somewhere and try to lock my car that I realize I don't have my key with me.

 

I assure you there is no key in my car. In fact, it doesn't happen all of the time. There are times it won't start. Also, my key fob had a low battery so there was even a period of time that I had to place my key in the "key cubby" so even being "in the car" was not enough to start it. Except for the handful of times it decides to start without the key at all!

 

I ran this test. Key placed within 3 feet outside of left side of car.
Window down. Car started.
Window up. [b]Key not detected.[b]

 

Now that fellow members have offered all their knowledge on this without satisfying you ("Give me some credit"), you appear to now have two choices...

1) If still under warranty, it's worth a trip to your MB dealer for a diagnosis... If the car starts with no key within 20 yards, it's a clear problem and the dealer's job to run it to ground (maybe in or out of warranty). But if your MB dealer can't duplicate the problem, they may charge you the overpriced "diagnosis charge"

2) As you have admitted, start carrying the key fob in your pocket. All the rest of us do.

 

That the OP's car can start without the key present is a serious malfunction that would have to be repaired if my car were involved.

I can't leave home without my key. As soon as I press the start button the alert will tell me that the key isn't in the car. Also I don't lock my car while it is in the garage. Its inconvenient if I need to put something in the glove box or something in the trunk to have to go get the key first. And I personally don't see any reason why a person determined enough to break into the garage to steal my car would be stopped by it being locked.

 

I agree with CarFan1 — this is a serious problem that demands an immediate fix for one reason:

if you can start the car without the key fob being present, then so can anyone.

Indeed, I have to wonder what your insurance company would say if your car were to be stolen and they found out that you have been aware of this problem.

 

Yes, the boundaries are not exact. If the key is close enough it will start. For example if I place mine on the pano roof then the engine starts, but if I place it on the metal roof then it doesn't. So yes if OP hangs their keys very close to the car, it might start in the garage, but as soon as they pull out the "key not detected" warning will light up in the instrument cluster. One has to blatantly ignore the warning to find themselves at their destination w/o the key. Now this is assuming there's no malfunction. If OP can start the car w/o a key anywhere nearby, then there's a serious issue.

I should also add, that the key fobs have motion sensors and go to sleep after two minutes if there is no motion. So if the key fobs are just hanging on the wall, they go to sleep and no longer send out a signal until they are woken up by motion. So it's even less likely that the car would start if the keys are hanging on the wall somewhere unless there happens to be an earthquake at the same time.

 

If you can't remember to pick up your key from the hook then the second easiest fix would be to remember to lock your car in the garage as well. That way you would have to get the key to get inside the car. If you have the Mercedes Me Connect app on your phone it will even remind you if you left your car unlocked.

 

yes, it is connected and reminds me. Which is great at the mall and work. I'm now immune to the notice when I get home.

 

They would write me a check. Same as they would if I left my keys in my car. Policies cannot exclude human error. Some do contain language about gross negligence, but that standard is so high to prove a quick search in my Westlaw could not find any cases in the last 20 years of an insurance company not paying due to customer error.

The theft aspect would seem like the most important thing, but it really isn't. As I said, every time it has happened, I discovered it when I arrived to my destination and reached in my pocket to lock the door and discovered my forgetfulness.

Of course this now has me curious. If my car thinks my key is there, will it unlock for anyone trying to open it? I'll have to test that next time it happens.

 

I always lock my car when left unattended - garage, service drive, or public parking. It is the safe and secure thing to do. A few years ago my home was burglarized while I was overseas. All the contents of my car including registration, tags, insurance id, stc. was taken. They couldn't steal the car without a key.

 

yeah, that's what perplexes me so much. There are times that it won't start. I then go back into my house and make my famous "dad joke" "well, my car won't start, I guess I'll try it with the key this time!" A joke I have made for years with all of my cars, but now, has a completely different meaning!

 

"Without satisfying me" uh? The first suggestion was asking if I checked if my spare key was in my "work bag." I think we can all agree, this isn't some random FB posting where people do have little to no knowledge. Most of us here have some basic understanding of our cars. My apologies if my silly joke offended you or anyone else.

As with most questions here, the answer can always be "go to the dealer." I was just posting the question here hoping someone else had a similar experience/solution which, as we all know, makes the trip to the dealer much smoother. I have seen on more than one thread where some dealerships could not pinpoint a solution but the collective experience/knowledge from people here have been helpful. As you noted, if I can go in with a defined problem that has been solved with a member here it can only save me money at my dealership.

 

So as I mentioned above, the key fobs for the W213 and all newer models have motion sensors in them. They go dormant after two minutes sitting still. This is a countermeasure against the increased relay attacks. You'd have to disturb the key fob on your way out to have a chance for the engine to start in case it's close enough.

 

If one stores the key fob on a hook close to the door entry to the garage, the keys can be awakened by vibration in the wall when the entry door is opened, or especially when the door is closed (soft slammed behind you).

Also, if the garage wall is shared with a kitchen on the other side (with a heavy, vibrating refrig/freezer nearby), or laundry room (where the washer/drier vibrate everything), etc, then your key fob will seldom go to sleep....

 

Like ua549, I always lock my car, even in the garage, but not for the most logical reason.

The questionable batteries in these cars have prompted numerous threads on how to conserve battery energy to avoid premature battery failure. Consensus of opinion is that the car "goes to sleep" more comprehensively when the car is locked, even though there are electrical systems that run 24/7, like that little cabin temperature sensor fan in the overhead console. (Get your ear close to hear the hum...)

As has been discussed numerous other times, keeping the keys on "a hook" within the garage makes the car maintain its alertness, because the car senses the key fob is nearby. This uses battery energy, too, not to mention exposing the car to relay theft.

Although this may not appear to answer OP's question, IMO it does in a way. Since you are considering development of new habits, I suggest locking the car, and storing the fob in your bedroom along with your wallet, other pocket goods, watch and cellphone. This means you will need the key fob on you to wake the car and unlock it, start the engine, etc., like everyone else.

Bottom line... So far no one has contributed that they have your same issue. So I think you can assume you have a unique situation that the dealer should diagnose, as it could be a faulty EIS (Elec. Ignition Switch) or Keyless-Go antennae system malfunction. Both have been mentioned in previous threads...

 

I think we can all agree that something very strange is going on here. Things don't really add up as portrait. As for keeping the car unlocked in the garage and draining the battery, that's a myth. Combined with the key fobs going to sleep there's really no negative impact. I've kept my cars unlocked in my garage for over a decade. What mostly drains the battery on these modern cars is the telematics combined with the always on cellular connection that stands by to receive remote commands from the phone app. You could actually argue that a locked car drains the battery even more, because the alarm system is active while the car is locked. For long term parking there's the standby mode that can be activated which turns off the online services as well as the alarm and any other consumers that normally stay powered. Even the door modules shut down after a while to preserve the battery and have to be woken up by pulling on the handle.

None of this really changes what's at odds here with this story. The fact that OP seems to be able to start the engine w/o a key fob nearby and seems to completely ignore the warning in the instrument cluster that the key can no longer be detected while driving away from the house. With a properly functioning vehicle, this doesn't add up.

 

I must say, I have never experience this or heard of anyone that has, but to think this is normal or you were lucky is not a response most people would expect. Are you saying you can start the car without the fob, go to Target, and realized you did not bring the fob and was still able to start the car again?

 

So here's my experience with the "myth"...

My main battery (W212) was replaced at the dealer under warranty in 2018. I've kept the car unlocked in the garage every night 2018-late 2021, though driving it just once a week or so. Every six weeks, I needed to put the battery on the external charger due to low charge. Once a month on the charger during Winter. Roughly 8-10 times per year.

The last year or so, based on advice read here, I started locking the car when not in use. The battery is now 5 years old, but I've needed to charge it only once (last February during the cold). My ECO Stop/Start regularly works (early on in each drive) now, and the Comand system resumes every time I start the engine. Same battery, much improved energy retention, and the only change in routine is locking the car. So, I'm sold on the new procedure, as NOT a myth. YMMV.

 

As they say, correlation does not imply causation. Your original battery was likely defective. I also don't drive my car very much. It sat in my garage for several weeks during the pandemic for example and I mostly only drive on the weekend. The Mercedes me app most of the time says my battery is partially charged and it takes a few days of driving for several hours before it shows as fully charged. Battery never went flat. I'll also submit the following screenshot. The nice thing about the standby mode is that it says exactly how long the car can be left w/o needing to charge the battery. As you can see, it's 21 weeks for my car. Now that was with a full battery after having it on the trickle charger overnight. I was going away for a month, so decided to fully charge the battery before leaving. W/o hooking it up to the trickle charger beforehand, it usually says I have about 7 weeks. My car is 4.5 years old now with the original battery and never locked while parked in the garage.

One of the things that many don't realize is that the AGM batteries that are in today's cars charge much slower than the lead acid batteries of yesterday, but they deal much better with the power demands of today's electronics in cars. It's pretty much normal that the battery is rarely fully charged, partly because modern cars even w/o mild hybrid have a certain level of recuperation via the alternator when coasting and they later use that energy to power things like the electric power steering, oil pumps etc., and decouple the alternator from the engine to save fuel . Beyond AGM batteries, lithium batteries are even deliberately kept at partial charge because it extends their longevity. Most people who give battery advice still think in terms of lead acid batteries of the past and don't really understand AGM and lithium batteries.

If you are such an infrequent driver, then the standby mode is what you should be using instead of worrying about locking the car in your garage. Actually never mind. Just realized you have a W212. This is the W213 forum. We are talking about newer cars, although I reiterate that I left my cars unlocked in my garage since the early 2000s, albeit initially with remote unlock key fobs, and not keyless go type key fobs, but my current car and previous car had keyless go. The keyless go feature in the W212 is likely more power demanding than in newer cars.