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Key unlocks doors but wont start car

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Old 08-19-2011, 09:26 AM   #1
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Key unlocks doors but wont start car

I recently dropped my keys (as I have many times before) but right after this drop, they keys wont start my car anymore. The remote lock/unlock works perfectly, but when I insert the keys into the ignition, there is no whirring sound and I cant turn the switch either.

Ive dismantled the key and nothing is loose/broken.

Im surprised that the door lock/unlock works while the ignition doesnt. Anyone know which part of they key is responsible for ignition?

I have a spare key so Im OK for now, but Id like to get this fixed in case I drop my second key..LOL. Ill try to get pics up soon...meanwhile anyone been through this before?

Thanks.
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Old 08-19-2011, 10:03 AM   #2
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It sounds like you messed up the part which communicates to the ignition. I don't know what you could do to fix it that wouldn't cost more than a replacement, though.

If you do get a replacement, and it's the new style - don't drop that. My "Panic" button plastic came off about 2 weeks ago.
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Old 08-19-2011, 12:52 PM   #3
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Quote:
Originally Posted by tommy View Post
It sounds like you messed up the part which communicates to the ignition. I don't know what you could do to fix it that wouldn't cost more than a replacement, though.

If you do get a replacement, and it's the new style - don't drop that. My "Panic" button plastic came off about 2 weeks ago.
Heyy tommy,

Yeah replacing it is as expensive as it can get....but I figured this would be the perfect opportunity to try to do the microchip swap into the new style key (which I can get off ebay for cheap).

I wonder if the ignition thing not working is a microchip fault or a sensor/transmitter failure. Im gonna look around on ebay for cheap keys.
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Old 08-19-2011, 02:09 PM   #4
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The key generates an infra red signal to unlock the ignition and activate the windows/moonroof remotely. The door lock/unlock remote is an RF signal. Looks like you broke something in the IR circuit when you dropped it?
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Old 08-21-2011, 03:07 AM   #5
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Try this test. Turn on your cell phone camera and point the red window in the nose of the key at the camera lens. Press and hold the lock or unlock button. Does the led inside the key illuminate? If yes, the RF and infrared portion of your key is fine. If the doors unlock with the key, then the EIS thinks it is your key.

The system is designed so that you could have a bad key battery, and still start the car. You can open the door with the cut metal key inside the key assembly. Inside the EIS there is a transformer primary. The secondary is located inside the key. When the key is inserted in the dash an AC voltage is connected to the primary. Inductance carries the current into the secondary in your key. The current is rectified and used to power the key to turn on the LED that you saw when pressing the buttons. Since your other key works, we can assume that the EIS in the dash is fine. If you saw the LED with your camera, the infrared transmitter is fine.

The problem lies in the secondary of the transformer in the key. The secondary is a coil of wire wrapped around a powdered iron core. Aside from the battery, it is the heaviest item in the key. It is most likely to be jarred lose when dropped. Use a 10X loupe to examine the circuit board. Look for the inductor in the nose and be sure it is well soldered. Simple to fix but you need someone with a surface mount soldering station. Good luck!
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Old 08-21-2011, 08:42 AM   #6
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Guys - Just so you understand the inductively energised key, handshake & start process.









Attached Thumbnails
Key unlocks doors but wont start car-inductive-key-1.jpg   Key unlocks doors but wont start car-inductive-key-2.jpg   Key unlocks doors but wont start car-inductive-key-3.jpg   Key unlocks doors but wont start car-inductive-key-process.jpg   Key unlocks doors but wont start car-inductive-key.jpg  


Last edited by Glyn M Ruck; 08-21-2011 at 09:35 AM.
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Old 08-21-2011, 09:31 PM   #7
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Thanks for the help guys and the pictures Glyn.

I did the camera phone test and I can see one of the transmitters blinking. Ive labelled it in the attached pictures.

Im assuming that this is the transmitter used to lock/unlock the doors which works fine, as the key does lock/unlock the doors.

However the ignition does not work, which like Moviela suggested might be caused by the induction coil that can be seen in one of the pictures coming loose. I tried to shake it etc. but it seems to be soldered pretty tightly onto the board.

So I guess the question is, if I remove the microchip as depicted in the key upgrade DIY thread and put it in a new style key would it work? I dont have access to surface mount soldering equipment, but I can always look around and see if I find someone who does.



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Key unlocks doors but wont start car-img-20110821-00068.jpg   Key unlocks doors but wont start car-img-20110821-00069.jpg  
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Old 08-22-2011, 12:58 AM   #8
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That is the secondary in the picture. Right under is a fairly large capacitor I suspect is used to smooth the output of the coil. It is also rather heavy, and could be broken loose. Look carefully for hairline cracks on the solder fillet at both ends.
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Old 08-22-2011, 08:29 AM   #9
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You're in good hands with Movie. Good luck. This is turning into a good reference thread. There has to be a dry joint or crack there somewhere.
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Old 12-19-2011, 12:42 PM   #10
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hi can anyone help me please i have the similar problem the only thing is my car starts but you need to play up with the key and ignition to start it does anyone knows what could it be? thanks alot
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Old 12-19-2011, 04:15 PM   #11
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Does this happen with both your keys? You could have a bad key that is effecting the handshake or an EIS on the way out. Are the IR windows in the nose of the key & the EIS clean? Does the steering lock release every time you insert the key without turning?
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Old 12-19-2011, 05:01 PM   #12
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hi i have only one keyand when i put it in nothing happens weel lock doesnt unlock it does nothing im just keeping puting it in and out for several times i would say about 10-20 times and it react once unlocking the weel lock and starting the engine
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Old 12-19-2011, 05:04 PM   #13
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and as i said my wife took it to a local car wash washed the engine and on the way back she says the dash board gone dark nothing has been working for a wile like indicators after a minute everything come back again and when she got home she says she couldnt get the key out and this all for me started from there and since then i have this problem getting worse
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Old 12-19-2011, 06:18 PM   #14
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Quote:
Originally Posted by astamir View Post
hi i have only one keyand when i put it in nothing happens weel lock doesnt unlock it does nothing im just keeping puting it in and out for several times i would say about 10-20 times and it react once unlocking the weel lock and starting the engine
OK - that is what I wanted to know. So we are not reliably achieving the handshake. See my explanation earlier in the thread. One of two problems. The key - or the EIS. Take the key apart & look for damage, solderwork loose or a crack in the board. Buy a new key. If this does not work you need a new EIS which is very expensive.

I recommend you get the car onto a Star diagnostic machine to ensure there is nothing else wrong as well.

Your basic problem is no reliable handshake between key & EIS.

Last edited by Glyn M Ruck; 12-20-2011 at 11:33 AM.
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Old 12-20-2011, 12:42 AM   #15
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Glyn do you think the engine wash could be related? like water in the front sam box?
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Old 12-20-2011, 10:35 AM   #16
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Trey - It's possible that the engine wash caused havoc. The front SAM should not get wet with it's snap cover but who knows. All that is required to enable start is RPM from CPS, Temp signal from the temp sensor/sender & correct key identification.

This could be coincidental to engine wash & now seems & EIS/Key issue due to unreliable release of steering lock.

It would do no harm to check that everything is dry, and that fuses 31,52 & 57 are dry & intact.

You know I frequently warn against engine washing. The EIS is top of the control pyramid & a short in the engine bay could damage it.
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Old 12-20-2011, 10:43 AM   #17
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done the diagnostic today and it showed the electronic ignition switch going to find the none dealer garage that can sort it out
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Old 12-20-2011, 10:46 AM   #18
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Sorry to hear that because the EIS is an expensive part but at least you know what is wrong.
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Old 12-20-2011, 10:49 AM   #19
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True dat, Glyn.
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Old 12-20-2011, 11:54 AM   #20
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the electrician guy said he know some places here in london that can do it cheaper than a dealer hopefully around 500-700 but my advise to anyone who want to buy the c class STAY AWAY FROM C CLASS MERCS!!!!!
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Old 12-20-2011, 12:09 PM   #21
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All Mercs use the same EIS. This is a potential issue with all modern cars. Don't do anything that might harm the electronics.

Washing modern engines is a no-no!
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Old 12-20-2011, 02:37 PM   #22
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Wait so you spray under the hood with water and that causes and electrical failure, and so you say to stay away from the C-class? logic fail.
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Old 12-20-2011, 02:48 PM   #23
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if you would read the people posts here who didnt wash the engine but still got this problem you wouldnt say that logic failed. and the electrician guy said that its a common place for c class that guy has 15 years expiriense
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Old 12-20-2011, 03:05 PM   #24
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Quote:
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if you would read the people posts here who didnt wash the engine but still got this problem you wouldnt say that logic failed. and the electrician guy said that its a common place for c class that guy has 15 years expiriense
Come off it. Every Mercedes uses an EIS now and they have for the past decade (though the ML was late to the game). Do you realize how many EISs are out there? Components fail. Yours might not have had your wife not insanely sprayed water all under the hood.

It sucks that it happened to you, but the "avoid C-class" comment was ignorant.
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Old 12-20-2011, 03:57 PM   #25
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thw water spray under the hood didnt cause the problem anyway as you say if there is so many EIS on mercs why on other classes this problem doesnt happen? im just asking dont wanna say anything with it. why this problem happens only with c class i red quote here that the guy who had BMW for 30 years and now decided to try MB has got this problem on c class i understand his frastration because i was dreaming about the mercs since im 5 yo now i got this c class and me with the other MB users got this problem only on c class. i have an E class 2003 e320 and that is brilliant always loved the MB and always will
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