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2001 C240, 2011 Honda Pilot, 2013 328i
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Discussion Starter #1
Hello everybody.

After spending almost $600 on spark plugs, wires, transmission fluid change, Coolant, etc. basically maintence. I have a new problem

When i try to use the electronic key, it will not unlock or lock the car. even the light on the key wont light up, The wierd thing is the key is making the car alarm go off. Bought new batteries and tried, same thing.

So after letting the alarm turn off after open the door with the mechanical key, i try to start the car but the key wont turn in the ignition. (left me stranded at publix for almost an hour, until it finally turned and started.

What is causing this.

P.S. Only have one key

(i couldnt find another thread, relating to my problem)
 

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W163 ML320, W203 C320, w204 c350 Sport
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32 Posts
Strange one. No matter what you press on the key it doesn't do anything?

Mine did the same when it ran out of battery but seems you have tried that too.
 

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Coupe/Convertible Forums Moderator
CURRENT: 2011 SL550, 2011 C300 FORMER: ML350, CLK550 Cabriolet, C240, ML320, 300TD
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If the red LED on the key itself does not light up when you press its buttons, then it's either a bad battery in the key, or the key is fried. Note that the key's battery has nothing to do with starting the engine - that uses and inductive circuit in the ignition switch to supply power so the key will work even without its battery. Another issue could be the vehicle battery. When it goes bad, you can experience some really odd electrical behavior.

Oh, and make sure you check the contacts in the key's battery carrier - they get dirty can can even get loose and not work. If you suspect a bad key, and especially since you only have one, you can order a new one from the dealer. Go to the parts counter with your ID and proof of ownership (tag receipt) to order an "additional key". It will cost around $250, but you'll get the shiny new "chrome" key, and it comes pre-programmed to work - no service visit required (unless you want them to disable any missing keys).
 

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2017 GLC 300 4Matic fully loaded... but for the heated steering wheel. Stupid previous owner! 😠
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1,138 Posts
the key's battery has nothing to do with starting the engine - that uses and inductive circuit in the ignition switch to supply power so the key will work even without its battery.
Yeah, right.

Then I step outside and try it my self.

Yeah, you're right.

:thumbsup:
 

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Get ready to swallow hard, went to the dealer for a new key for mine and turns out they cost $220 for new key for C240???:crybaby2:
 

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Well I figured out my problem .. $239.. For a new key and now everything works good.. Apparently the key had gotten wet which caused it to lock up the system when I put the key in the ignition.. But now I'm having problems with CEL it says something about the fuel trim do y'all know about that?
 

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Coupe/Convertible Forums Moderator
CURRENT: 2011 SL550, 2011 C300 FORMER: ML350, CLK550 Cabriolet, C240, ML320, 300TD
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Yes, replacement SmartKeys are expensive. If you just want a "spare" and don't want to deactivate a lost key, then you can just go to the parts counter and order one with your IN and proof of ownership (i.e. vehicle registration receipt). It is around $250 (prices set individually by dealer). You will get the new "chrome" style key as they don't make the old all plastic ones anymore. If you have a good relationship with your dealership (bought the car there, always have it service there, etc.) you may be able to get a discount of 10%-20%. Otherwise, that's the price.

@ms.cedes: That fuel trim problem is often symptoms of a bad MAF sensor. A new one is over $200, but you might be able to fix it with a cleaning. MBZ MAFs are very sensitive, though so that often doesn't work or makes it worse. And don't try one of those cheap $80 MAFs on eBay - they won' work.
 

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Thanks for that.. I was looking at other post and it said the same thing but still not sure what MAF stands for.. Also it's making my car run a little different.. Where is this sensor located??
 

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CURRENT: 2011 SL550, 2011 C300 FORMER: ML350, CLK550 Cabriolet, C240, ML320, 300TD
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Yep, MAF = Mass Airflow, it's a sensor in the air intake that allows the ECU to determine the volume, temperature, and relative humidity of air entering the engine. That information is used to adjust the fuel mixture for proper combustion.
 

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One last question what causes the mass airflow sensor to go bad... I had put different gas in my car than I usually use.. Does that have anything to do with it??
 

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Oh when I say different gas I don't mean the grade of gas.. I always use premium.. But I have heard about stores with bad gas could cause problems
 

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CURRENT: 2011 SL550, 2011 C300 FORMER: ML350, CLK550 Cabriolet, C240, ML320, 300TD
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Probably not - no fuel actually goes through the MAF sensor - just air, since it's "upstream" of where the injectors put fuel into the mixture. MAF sensors usually go bad because of dirt buildup (hence the possibility that cleaning it will help) or just from age. The sensor is actually a wire that is heated, and then its resistance is measured as air flows across it and cools it. Through that electrical function, the ECU can tell how much moisture and how dense the air is. As it ages, the wire can get weak, stretch and start giving false signals.

In your case, maybe the fuel you used was bad and that has cause the rough engine troubles and the malfunction codes? Gasoline is more uniform today than it used to be, but still, a tank of "bad gas" is possible. If it goes away after a tank of fuel, then that's probably it. If not, then I'd pull codes and if it's still "fuel trim", I'd clean the MAF.
 

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2005 CLK500 w/30K
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Well I figured out my problem .. $239.. For a new key and now everything works good.. Apparently the key had gotten wet which caused it to lock up the system when I put the key in the ignition.. But now I'm having problems with CEL it says something about the fuel trim do y'all know about that?
Dead keys can frequently be fixed by a guy named drknight.

He moves the chip with the individual codes to a new Chrome key (used from Ebay, avtually) and BINGO, perfect working key.

I tried his method myself and it works great.

He has a service on Ebay but I am looking for people in LA area for FREE, just trying to get experience.
 

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Coupe/Convertible Forums Moderator
CURRENT: 2011 SL550, 2011 C300 FORMER: ML350, CLK550 Cabriolet, C240, ML320, 300TD
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In this case, transplanting the original key's chip might work.
 
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